673 Electronic and Computer Controlled Systems Technician Handbook 06-22-09
Short Description
Download 673 Electronic and Computer Controlled Systems Technician Handbook 06-22-09...
Description
Electronic & Computer Controlled Systems Course 673 Technician Handbook
© 2009 Toyota Motor Sales, U.S.A., Inc.
TOYOTA Technical Training
All rights reserved. This book may not be reproduced or copied, in whole or in part by any means, without the written permission of Toyota Motor Sales, U.S.A., Inc. Revision Date: June 22, 2009
Table of Contents 673 Electronic & Computer Controlled Systems Objectives
Final Student Performances ................................................................ a
Section 1: Diagnostic Techniques and Tools
Course Menu ....................................................................................... 3 Section 1 Topics .................................................................................. 5 Electronic Control Units ........................................................................ 6 How ECUs Work ................................................................................... 7 Logic Function .................................................................................. 7 Simple ECU Inputs ................................................................................ 8 Voltage ON/OFF (Switch) Input ........................................................ 9 Variable Voltage Input .................................................................... 10 Variable Resistance Input ............................................................... 11 Pulse Pattern Input ......................................................................... 12 Simple ECU Outputs ........................................................................... 13 Transistors as Switches .................................................................. 13 Pulse Width Modulation ...................................................................... 14 Duty Cycle ........................................................................................... 15 Power-Side Control ......................................................................... 16 Self Diagnosis ..................................................................................... 17 Differences in Self-Diagnosis .......................................................... 17 ECU Memory ...................................................................................... 19 Types of ECU Memory ................................................................... 19 Customization ..................................................................................... 20 Initialization ......................................................................................... 21 Why Initialize? ................................................................................. 21
Section 2: Overview of Multiplex Communication
Section 2 Topics ................................................................................. Why Use Multiplexing ......................................................................... Applications of Multiplexing ............................................................ Benefits of Multiplexing ................................................................... Multiplexing ......................................................................................... ECU Communication .......................................................................... Signaling Between ECUs .................................................................... Communication Protocols ................................................................... Multiplex Topology .............................................................................. Ring Topology ................................................................................. Two Opens in a Ring Network ........................................................ Open in a Star Network .................................................................. Open in a Bus Network ................................................................... Single Wire vs. Twisted-Pair ............................................................... Advantage of Twisted-Pair Wiring ..................................................
23 24 24 24 25 26 27 28 29 30 31 32 33 34 35
Section 3: Signals & Waveforms
Section 3 Topics ................................................................................. Electronic Communication .................................................................. Types of Waveforms ....................................................................... Waveform Measurements ................................................................... Amplitude ........................................................................................
37 38 38 39 39
Technical Training
i
Table of Contents 673 Electronic & Computer Controlled Systems Frequency ....................................................................................... 40 Pulse Width ..................................................................................... 41 Duty Cycle ...................................................................................... 42 Section 4: Measuring Signals
Section 4 Topics ................................................................................. The Oscilloscope ................................................................................ PC Oscilloscopes ................................................................................ Basic Operation .................................................................................. Oscilloscope Scales ............................................................................ Repair Manual Suggested Scales .................................................. Repeating vs. Changing Patterns ....................................................... Capturing Waveforms ......................................................................... Scope Pattern Comparison ................................................................. The Effect of Scale .............................................................................. Trigger Function .................................................................................. Other Trigger Uses ............................................................................. Advanced DVOM Features ................................................................. MIN/MAX Recording ....................................................................... Peak MIN/MAX ............................................................................... Relative Delta ................................................................................. Frequency Measurement ................................................................ Duty Cycle ...................................................................................... Worksheet: DVOM Set-up & Advance Features ................................. Instructor Demo: Using DVOM Resistance Setting ............................
43 44 45 46 47 48 49 50 51 52 53 54 55 55 55 55 56 56 57 58
Section 5: Using a PicoScope™
Section 5 Topics ................................................................................. Introduction to PicoScope™ ................................................................ Connecting the Leads ..................................................................... PicoScope Features ........................................................................... Auto Voltage Scale ......................................................................... Auto Setup ...................................................................................... Manual Voltage Scale Settings ....................................................... Manual Time Scale Settings ........................................................... Turning the Trigger On ................................................................... Setting the Trigger .......................................................................... Start and Stop Capturing ................................................................ Horizontal Zoom ............................................................................. Rulers ............................................................................................. Sample Rate ................................................................................... Displaying Two Channels ............................................................... Separating the A-B Traces ............................................................. Printing, Saving and Sending Patterns ........................................... Worksheet: In-class PicoScope: Basic Set-up .................................... Worksheet: Using DVOM & PicoScope .............................................. Instructor Demo: PicoScope & Power Window Circuit .......................
59 60 60 61 61 61 62 62 63 64 65 66 67 69 70 71 72 73 74 74
ii
Technical Training
Table of Contents 673 Electronic & Computer Controlled Systems Section 6: Using an Inductive Clamp
Section 6 Topics ................................................................................. The Inductive Clamp ........................................................................... Polarity ............................................................................................ Current Rating ................................................................................ Preparation for Use ......................................................................... Converting Measurements to Amps ............................................... Amp Clamp Applications ..................................................................... Diagnosing Short Circuits and Parasitic Draw ................................ Diagnosing Motor Faults with an Oscilloscope ............................... Worksheet: Inductive Current Clamp I: Measurement & Conversion . Worksheet: Inductive Current Clamp II: A/C Blower Motor .................
Section 7: Multiplex Circuit Diagnosis
Section 7 Topics ................................................................................ 83 Additional Properties of MPX Protocols .............................................. 84 Communication Direction ................................................................ 85 Transmission Timing ....................................................................... 86 Collision Detection .......................................................................... 87 Data Casting ................................................................................... 88 Sleep Mode ..................................................................................... 89 Wakeup Function ............................................................................ 89 Body Electronics Area Network .......................................................... 90 Local Interconnect Network ................................................................ 91 LIN Characteristics ......................................................................... 91 LIN Replacing BEAN ...................................................................... 91 LIN Gateway Function .................................................................... 92 Controller Area Network ...................................................................... 93 Terminating Resistors ..................................................................... 93 Audio Visual Communication-Local Area Network ............................. 94 AVC-LAN Protocol .......................................................................... 95 Gateway ECU ..................................................................................... 96 CAN Gateway ECU ........................................................................ 96 Summary of Gateway ECU Functions ............................................ 97 CAN Gateway ECU Functions ........................................................ 98 Transmit/Receive Charts .................................................................... 99 BEAN Signal ..................................................................................... 100 BEAN Diagnosis ............................................................................... 101 Open Circuit .................................................................................. 102 Short Circuit .................................................................................. 103 Short Circuit Step 1........................................................................ 104 Short Circuit Step 2........................................................................ 105 Short Circuit Step 3........................................................................ 106 Short Circuit Step 4........................................................................ 107 Short Circuit Step 5........................................................................ 108 Short Circuit Step 6........................................................................ 109 Diagnosing a Large Network ........................................................ 110 Diagnosing with Techstream ........................................................ 111 Diagnosing a BEAN Open Circuit with an Oscilloscope ............... 112
Technical Training
75 76 76 77 78 79 80 80 81 82 82
iii
Table of Contents 673 Electronic & Computer Controlled Systems
Section 8: Electronic Systems
iv
Worksheet: BEAN Network Diagnosis .............................................. Instructor Demo: BEAN Operation and Diagnosis ............................ LIN Signal ......................................................................................... LIN Diagnosis .................................................................................... Worksheet: A/C LIN Interface ........................................................... CAN Signal ....................................................................................... CAN Diagnosis ................................................................................. Short Between CANH and CANL ................................................. Short to B+ or Ground ................................................................... Opens ........................................................................................... CAN Bus Check ............................................................................ Location of DLC3 .......................................................................... Terminating Resistors ................................................................... Resistance Tests on CAN Circuits ................................................ Worksheet: CAN Diagnosis ............................................................. Instructor Demo: CAN Resistance Test Precautions ........................ Worksheet: CAN Main Bus Faults ................................................... Worksheet: CAN Sub Bus Diagnosis ............................................... AVC-LAN Signal ............................................................................... AVC-LAN Diagnosis .......................................................................... AVC-LAN DTCs ............................................................................ Worksheet: AVC-LAN Inspection ...................................................... Other Multiplex Circuits ..................................................................... A/C Servo Motor Circuits .............................................................. BUS Connectors ............................................................................... Pulse-Type Servo Motors ................................................................. Worksheet: A/C Bus Servo Motor Operation & Diagnosis ................
113 113 114 115 116 117 118 118 118 119 120 120 121 122 124 124 125 125 126 127 128 129 130 130 131 132 133
Section 8 Topics ............................................................................... Engine Immobilizer Function ............................................................ Engine Immobilizer Operation .......................................................... Key Code Registration ...................................................................... Master Keys and Sub Keys .............................................................. Automatic Key Code Registration ..................................................... Watch for Error Codes .................................................................. Ending Automatic Registration ..................................................... Configuration in Earlier Models ......................................................... Configuration in Later Models ........................................................... Immobilizer Reset ............................................................................. Immobilizer Reset Support Chart ...................................................... ECU Communication ID Registration ............................................... Be Wary of Differences between Models .......................................... Analyzing ECU Input and Outputs .................................................... Transponder Signals ..................................................................... Power and Ground Circuits ........................................................... Terminal Values and Conditions ...................................................
135 136 137 137 138 139 139 139 140 141 142 143 144 145 146 147 148 149
Technical Training
Table of Contents 673 Electronic & Computer Controlled Systems
Appendix
Transponder Key Amplifier Terminal Values ................................. ECM Terminal Values ................................................................... Worksheet: Immobilizer .................................................................... Power Distributor ............................................................................. Protect Mode ............................................................................... Mode Monitor Terminal ................................................................ Smart Junction Box (MICON) ........................................................... High Intensity Discharge (HID) Headlights ....................................... Dynamic Laser Cruise Control Operation ......................................... Laser Sensor ..................................................................................... Indicators ......................................................................................... Error/Cancellation Codes .................................................................. Constant Speed Control .................................................................... Decelerator Control............................................................................ Follow-Up Control .............................................................................. Accelerator Control ........................................................................... System Diagram ............................................................................... Distance Control ECU Waveforms .................................................... Laser Radar Sensor Waveforms .......................................................
150 151 152 153 153 153 154 155 156 157 158 158 159 160 161 162 163 164 165
Appendix ........................................................................................... Transistors ........................................................................................ Transistor Types ........................................................................... How a Transistor Works ............................................................... Transistor Switches ...................................................................... Transistor Amplifiers ..................................................................... Digital Circuits ............................................................................... Analog-to-Digital Converter .......................................................... Logic Gates ....................................................................................... Normal CAN Signal ........................................................................... CAN Shorts and Opens .................................................................... Short CANH to CANL ................................................................... Short CANH to B+ ......................................................................... Short CANL to B+ ......................................................................... Short CANH to Ground ................................................................. Short CANL to Ground .................................................................. Open in CANH or CANL (Main Bus) ............................................. Open in CANH and CANL (Main Bus) .......................................... BEAN Signals ................................................................................... BEAN Short to Ground ................................................................. Normal BEAN, Dual Trace ................................................................ BEAN Open Circuit, Dual Trace ...................................................
167 168 169 170 171 172 173 174 175 176 177 177 178 178 179 179 180 181 182 183 184 185
Worksheets
Technical Training
v
Table of Contents 673 Electronic & Computer Controlled Systems
This page intentionally left blank.
vi
Technical Training
Objectives 673 Electronic & Computer Controlled Systems Course 673 Electronic & Computer Controlled Systems Final Student Performances Terminal Objective (Terminal FSP) Given all of the applicable tools, equipment, and appropriate vehicles, the technician will be able to apply a number of diagnostic techniques to monitor and repair faults in advanced computer and electronic circuits. Technician Objectives (FSPs) The technician will be able to: 1. Research information related to: • The purpose and function of ECU terminals • Inputs & Outputs • Terminals of the ECU • Power & Ground points 2. Identify inputs and outputs and determine how they affect ECU operation. 3. Differentiate between: • Pulse width & duty cycle • Frequency & duty cycle 4. Identify the consequences of the following to the diagnostic process: • Initialization (Memory Loss) • Customization (CBEST) • Sleep mode vs. normal operation 5. Demonstrate proficient use of the advanced DVOM features. • MIN/MAX function • Peak MIN/MAX function • Measure frequency • Measure duty cycle 6. Apply advanced DVOM functions for quick diagnostic evaluations. 7. Practice using an Inductive Current Clamp with a DVOM to provide the ability to take current readings without breaking into a circuit. 8. Utilize an inductive Current Clamp to evaluate system operation & determine diagnostic strategy. 9. Practice conversion of voltage and amperage values to apply to inductive clamps that use conversion factors for sensitivity. 10. Monitor AC blower motor current using a DVOM equipped with an inductive current clamp, and monitor current using an oscilloscope and inductive clamp.
Technical Training
a
Objectives 673 Electronic & Computer Controlled Systems 11. Properly set-up an oscilloscope • Auto features • Voltage & Time Scale Settings • Horizontal & vertical rulers • Trigger point • Horizontal & vertical zoom features 12. Apply the basic features of the oscilloscope used in combination with the Techstream Unit. 13. Locate and back probe a dimmer-controlled interior lamp or LED, practice measuring Voltage (V), Hertz (Hz), and percentage values (%) using a DVOM, and use an oscilloscope to display the signal pattern. 14. Set oscilloscope voltage and time settings appropriate to the circuit measured. 15. Utilize oscilloscope patterns derived from a known good vehicle to verify normal system operation. 16. Differentiate between different oscilloscope patterns. 17. Use an oscilloscope to confirm proper operation vs. a faulty circuit • Duty cycle • Frequency • Amplitude 18. Use an oscilloscope to identify intermittent faults. 19. Capture, record, save and send oscilloscope waveforms. 20. Identify Body Electronics Area Network topology and network operation. 21. Perform fault diagnostics on a BEAN network. 22. Identify Local Area Network topology and network operation. 23. Monitor and diagnose the AC Control Assembly operation and LIN communication using Techstream, an oscilloscope and TIS. 24. Identify Controller Area Network topology and network operation. 25. Use an ohmmeter and an oscilloscope to observe CAN High and CAN Low; diagnose a short to ground and an open circuit on CAN High and CAN Low; and short CAN High to CAN Low to observe the results. 26. Develop a strategy to diagnose a CAN Network fault using the EWD, a Techstream CAN Bus Check, and the information provided. 27. Identify Audio Visual Communication-Local Area Network topology and network operation. 28. Create, monitor and diagnose an AVC-LAN System amplifier malfunction using Techstream and an oscilloscope. 29. Monitor AC bus and servo motor operation using Techstream DATA LIST and an oscilloscope to deduce communication problems with the AC System. 30. Reference service literature to determine if immobilizer reset is supported on a vehicle. 31. Use Techstream Data List to make determinations related to the ID Code of the transponder chip embedded in the ignition key of the Immobilizer System. 32. Use an oscilloscope to observe Immobilizer System waveforms under varying conditions and compare them to those found in the Repair Manual.
b
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
673 Electronic & Computer Controlled Systems
Welcome Toyota Technicians
Technical Training
1
673 Electronic & Computer Controlled Systems
Technician Handbook
This Page Intentionally Left Blank
2
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Course Menu Electronic & Computer Controlled Systems • Electronic Control Units • Overview of Multiplex Communication • Signals & Waveforms • Measuring Signals • Using a PicoScope™ • Using an Inductive Clamp • Multiplex Circuit Diagnosis • Electronic Systems
A
Technical Training
Appendix
• Transistors • CAN Waveforms • BEAN Waveforms
3
673 Electronic & Computer Controlled Systems
Technician Handbook
This Page Intentionally Left Blank
4
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 1 Topics
Electronic Control Units
Technical Training
• Electronic Control Units • Logic Function • Simple ECU Inputs • Simple ECU Outputs • Self-Diagnosis • Memory • Customization • Initialization
5
Technician Handbook
673 Electronic & Computer Controlled Systems
Electronic Control Units Electronic Control Units (ECUs) are small computers programmed to perform specific automotive functions. What are some typical automotive ECUs?
ECUs use electronic components in integrated circuits to perform their functions.
Electronic Control Units
In the 1970’s, the decreasing cost and increasing power of computerized microprocessors launched the personal computer industry. Because of their speed and flexibility in carrying out complex functions, microprocessors were adapted for hundreds of uses beyond personal computers. The first microprocessors began appearing in automotive engine control systems in the early 1980s. In automotive applications, they became known as electronic control units (ECUs). Today, some vehicles may have dozens of ECUs controlling a wide variety of vehicle systems, including: • engine controls • transmission • braking • steering • air conditioning • door locks • suspension • cruise control • tire pressure monitoring • and many other systems.
6
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
ECU Logic Function ECUs have electronic logic circuits that “make decisions” by evaluating conditions according to predetermined rules. Light Control SW Headlights Light Control Sensor
Body ECU
How ECUs Work
Conditions
IF Light control switch is in the AUTO position and Light control sensor detects LOW ambient light and Ignition switch is ON
Decision
Taillights
THEN Turn headlights ON Turn taillights ON
An ECU is a small computer programmed to perform a specialized function in the vehicle. As with any computer, it operates on the principle of input, processing, and output. Input – Information about conditions is supplied to the ECU as input signals. Input can be provided by: • sensors • switches • other ECUs. Processing – The ECU analyzes the input signals. Based on its programming, it determines what output signals to send, if any. Output – Vehicle systems are controlled by the ECU output signals. These signals may cause a motor to operate, a light to come on, or some other operation of a vehicle component.
Logic Function
For an example of the ECU’s logic function, consider the lighting control system which is within the Body ECU. A simple lighting control system uses three inputs – the light control switch, the light control sensor, and the ignition switch. When the condition of these three inputs matches the conditions preprogrammed in the ECU, the ECU turns on the headlights and taillights.
Technical Training
7
Technician Handbook
673 Electronic & Computer Controlled Systems
Simple ECU Inputs Voltage ON/OFF
Voltage Pulse Pattern
Combination Switch
Active Speed Sensor
MRE A MRE B
Sensor IC
Variable Voltage Variable Resistance
What are some other types or examples of ECU inputs?
Oxygen Sensor Temp Sensor Exhaust Gas
Simple ECU Inputs
Signals from switches and sensors can supply information to the ECU in several ways. Voltage ON/OFF – A simple switch opens or closes a circuit. It is the presence or absence of voltage in the circuit that signals the ECU. Variable Voltage – Some sensors produce a voltage that changes depending on the conditions the sensor is measuring. The amount of voltage produced at any given moment provides information about the condition at that time. Variable Resistance – In other types of sensors, electrical resistance increases or decreases as external conditions change. Sensing the changing voltage as a result of changing resistance in the circuit signals the ECU what the conditions are. Variable Pulse Pattern – Another method for signaling the ECU about changing conditions is to turn a circuit on and off rapidly at a particular frequency. This works especially well for signaling rotational speed. It is the frequency of the ON/OFF pulses that supplies information to the ECU.
8
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Voltage ON/OFF (Switch) Input The ECU detects the state of a ground-side switch by reading the circuit voltage. When switch ON is detected, the ECU performs a function, such as turning on a lamp. B+
B+ OFF: V = 12.6V (open circuit voltage)
0V
ECU 12.6V
Ground-side switched
12.6v
ON: V = 0.1V (available voltage)
*
5V
ECU 12.6V
0.1v
*
Voltage can also be measured at the ECU terminal.
* Conceptual illustration only
Voltage ON/OFF (Switch) Input
The diagrams above illustrate a ground-side switch connected to an ECU. The ECU supplies battery voltage to the switch circuit and provides the circuit’s load (a resistor). The ECU’s electronic circuits detect when the voltage after the load is high (near battery voltage) or low (near ground voltage). While the switch is open, no current is flowing and the available voltage after the load is near battery voltage. When the switch is closed, current flows and most of the battery voltage is dropped across the load. The available voltage after the load is now near ground voltage. In this example, the switch controls a lamp, but is not actually part of the lamp circuit. When the ECU senses a voltage drop in the switch circuit, it supplies five volts to the transistor. This in turn closes the lamp circuit, lighting the lamp.
SERVICE TIP
NOTE
Technical Training
You can detect the same high or low voltage the ECU is detecting by measuring voltage at the appropriate ECU terminal. If the switch is closed and the voltage remains high, you’ll know there is an open in the circuit between the ECU and the switch. The actual wiring inside the ECU is extremely complex. The ECU circuit details shown in the diagrams above and the diagrams on the following pages are to illustrate concepts, not actual internal connections.
9
Technician Handbook
673 Electronic & Computer Controlled Systems
Variable Voltage Input The oxygen sensor is a voltage generator. The engine control module interprets the voltage to make corrections to the air-fuel ratio.
Voltage V
Atmosphere
ECM V > 0.45v : air-fuel ratio too rich V = 0.45v : air-fuel ratio correct V < 0.45v : air-fuel ratio too lean
Exhaust Gas
Variable Voltage Input
An oxygen sensor is a voltage generator, producing between 0.1v and 0.9v depending on the oxygen content of the exhaust gas compared to the atmosphere. The engine control module’s electronic circuits measure the amount of voltage generated by the oxygen sensor, and use that information to control the air-fuel ratio.
10
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Variable Resistance Input
A temperature sensor is a type of variable resistor. Its resistance changes with temperature.
12.6V or 5V V
An ECU can detect the change in the sensor’s resistance by measuring voltage.
ECU
Variable Resistance Input
A temperature sensor is a type of variable resistor whose resistance changes with temperature. This type of sensor is often called a thermistor. Two types of thermistor are: Positive temperature coefficient (PTC) thermistor – resistance increases as temperature increases Negative temperature coefficient (NTC) thermistor – resistance decreases as temperature increases Thermistors are commonly used for engine coolant temperature sensors and ambient temperature sensors. Modern Toyota vehicles use NTC thermistors exclusively.
Technical Training
11
Technician Handbook
673 Electronic & Computer Controlled Systems
Pulse Pattern Input An active wheel speed sensor generates a series of voltage pulses as the wheel rotates. MRE A MRE B
Sensor IC
As rotation speed increases, pulses are generated at a higher frequency. The ECU measures the pulse frequency to calculate vehicle speed.
Voltage
Voltage Lower Rotation Speed
Time
Pulse Pattern Input
Higher Rotation Speed
Time
Another type of ECU input is a pulse pattern. When voltage rises momentarily, then falls, the transient voltage reading is called a pulse. When a component creates multiple pulses, the result is a pulse pattern (or pulse train). An active wheel speed sensor is a component that generates a pulse pattern. A magnetic ring mounted on the wheel hub has alternating north-south fields that are detected by the sensor pickup. As the wheel rotates, the alternating magnetic fields are converted into a series of voltage pulses. The frequency of the pulses increases with the wheel rotation speed. When the pulse pattern is provided as ECU input, the ECU’s circuits are able to measure the pulse frequency and calculate wheel RPM and vehicle speed.
12
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Simple ECU Outputs When the operating conditions are met, the ECU makes a connection to power or ground to energize a circuit ECU NPN
B+
How a Transistor Works (NPN) Transistor
5V
Ground-side controlled circuit ECU B+
Collector When voltage is applied to the base… ...current can flow from the collector to the emitter
Base
PNP
Emitter
Power-side controlled circuit
A
See Appendix for More Info
Simple ECU Outputs
The simplest way for an ECU to control a vehicle function is to turn a circuit on or off. A circuit can be ground-side switched or power-side switched.
Transistors as Switches
Electronic circuits use transistors for switching circuits on and off. A transistor is a solid-state electronic component having a base, collector and emitter. In the more commonly used NPN transistor, when sufficient voltage is applied to the base, current flows from the collector to the emitter. One of the advantages of the transistor is that a low voltage at the base is able to control a large current flowing through the collector and emitter. In that respect, a transistor is similar to a relay. Some transistors also regulate current flow based on the amount of voltage applied to the base. Within the transistor’s limits, a higher base voltage results in a greater flow of current through the collector/emitter. This feature is used in amplifier circuits where the low voltage signal from a microphone regulates current flow in higher power speaker circuits
Technical Training
13
Technician Handbook
673 Electronic & Computer Controlled Systems
Pulse Width Modulation The ECU can open and close a circuit rapidly to control component operation. The process of varying the amount of time a circuit is ON is called pulse width modulation. Example Voltage Pulses
The ECM regulates the injector ON time by regulating the width of the voltage pulse to the injectors.
Pulse Width Notice the pulse width increases at higher load as the ECM increases the injector ON time.
Pulse Width Modulation
An ECU’s electronic circuits have the ability to open and close a circuit very rapidly. The ECU can switch a circuit on for a fraction of a second at very precise intervals. When a circuit is switched ON and then OFF, the momentary change in voltage creates a voltage pulse. (The pulse can be either a momentary increase or decrease in voltage depending on whether the circuit is ground-side switched or power-side switched and where the voltage is measured.) When the voltage is viewed on an oscilloscope, the voltage pulse’s width represents the amount of time the circuit is switched ON and can be as brief as 1 millisecond or less. In some circuits, the ECU uses the amount of ON time to regulate component operation. When the ECU varies the width of the voltage pulse (the ON time) to control a component, the process is called pulse-width modulation.
NOTE
14
In the above example, the frequency of the pulses changes as well as the pulse width. In some circuits, the frequency of the pulses is constant.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Measuring Duty Cycle When the ECU modulates a circuit at a constant frequency, you can measure the circuit’s duty cycle. Duty cycle is the percentage of ON time compared to total cycle time.
Varying the duty cycle can vary the brightness of a lamp or the speed of a motor.
ECU B+
If the percentage of ON time decreases, the lamp becomes dimmer.
5V
12 V
12 V
0V
0V
1 cycle (100%)
75% ON (grounded)
1 cycle (100%)
25% ON (grounded)
In a ground-side controlled circuit, measure after the load.
Duty Cycle
The terms pulse-width modulation and duty cycle are often confused or used incorrectly. Pulse-width modulation is a function an ECU can perform to turn a circuit on and off rapidly to regulate the amount of ON time. As the pulse width changes, the frequency of the pulses might or might not change depending on the circuit design and intended operation. When a circuit is switched on and off rapidly at a constant frequency, duty cycle measures the percentage of ON time compared to total cycle time. If the circuit is ON 75% of the time, it is operating at a 75% duty cycle. When a circuit is duty-cycle controlled, the pulse frequency does not change – only the percentage of ON time. An ECU varies the duty cycle to control the speed of a motor or the brightness of a lamp by switching the circuit ON and OFF hundreds of times per second. Human senses can’t perceive a lamp or motor being cycled on and off that quickly. Nonetheless, the amount of power to the component increases or decreases depending on how much of the time the circuit is ON versus OFF. As OFF time increases, the net power supplied to a component decreases resulting in the lamp becoming dimmer or the motor running slower. As ON time increases, power increases and the lamp becomes brighter or the motor runs faster.
NOTE
Technical Training
When the circuit is ground-side controlled, voltage before the load is always battery voltage, and voltage after the switch is zero, or near zero. To observe voltage modulation, place the positive probe between the load and the switch (which may be an ECU).
15
Technician Handbook
673 Electronic & Computer Controlled Systems
Measuring Duty Cycle Signals in a power-side controlled circuit are the opposite of signals in a ground-side controlled circuit.
ECU B+ If the percentage of ON time decreases, the lamp becomes dimmer. 1 cycle (100%)
1 cycle (100%)
75% ON (powered)
25% ON (powered)
In a power-side controlled circuit, measure before the load.
Power-Side Control
Most circuits in Toyota vehicles are ground-side controlled. When a pulsewidth modulated circuit is power-side controlled, the voltage modulation is observable after the ECU and before the load. In this arrangement, the circuit is ON when the voltage rises. Note that if voltage is measured after the load, a very minute change in voltage occurs as the circuit is modulated. At this point in the circuit, voltage is zero when the circuit is open. When the circuit is closed, ground voltage is present. The difference is usually less than 0.1V and may not be observable depending on your scope settings.
16
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Self-Diagnosis The ECU’s internal wiring can be arranged so it can detect when an input circuit is open or shorted to ground. ECM
Throttle Position Sensor
Under normal conditions, the ECM senses more than 0V and less than 5V at VTA and VTA2.
VTA VC
5V
VTA2 E2
DTC
P0120
With either a short or an open in the input circuit, voltage at VTA and VTA2 becomes 0V and the ECU sets a DTC.
Throttle/Pedal Position Sensor/Switch “A” Circuit Malfunction
2002 Tundra V8
Self-Diagnosis
A significant reason ECUs have become so common in automobile systems is their ability to perform self-diagnosis. ECUs can identify faults in circuits, components, and even within the ECU itself. When a fault is detected, the ECU can: • Illuminate a warning light • Set a diagnostic trouble code • Begin operating in a fail-safe mode by: ◦ Disabling a system that is working incorrectly ◦ Using sensor data from alternate sources ◦ Applying alternate rules for operating the vehicle or subsystem to maintain maximum safety
Differences in SelfDiagnosis
An ECU’s self-diagnosis capabilities can range from very simple to highly sophisticated. Each ECU has its own features and limitations, and very few work in exactly the same way. The example above is a throttle position sensor circuit. The electronics inside the engine control module (ECM) are designed so that an open or a short to ground on VTA or VTA2 can be detected and a DTC set. The circuit arrangement inside the ECM is not able to distinguish a short from an open, however. In either case, the voltage the ECM is monitoring goes to 0V.
Technical Training
17
Technician Handbook
673 Electronic & Computer Controlled Systems
Self-Diagnosis ECUs can be wired so they can detect the difference between an open or short, and set a different DTC for each. ECM
Throttle Position Sensor
In this arrangement, what is the normal voltage at VTA1? What is the voltage with a short in the circuit?
VTA1 VC
5V
VTA2 E2
DTC
P0122
Throttle/Pedal Position Sensor/Switch “A” Circuit Low Input
DTC
P0123
Throttle/Pedal Position Sensor/Switch “B” Circuit High Input
Differences in SelfDiagnosis (Cont’d)
What is the normal voltage at VTA2? What is the voltage with an open in the circuit?
2003 Tundra V8
In this throttle position sensor circuit, the electronics inside the ECM are arranged slightly differently. In this arrangement, a short to ground on a VTA line causes the monitored voltage to go to 0V. An open in a VTA line, however, causes the monitored voltage to go to 5V. Thus, this ECM can distinguish between an open or short on an input circuit and can set a DTC for one or the other. The additional data supplied by the ECM makes it easier and faster to diagnose and correct the problem.
18
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
ECU Memory ECUs have different types of memory.
• DTCs • Driver preferences • Vehicle operating characteristics ECU program logic
ECU program logic, data (reflash)
B+
ECU Memory RAM (volatile) ROM (permanent) EEPROM (reprogrammable)
ECU Memory
Like other computers, ECUs have internal memory. Besides storing DTCs, they can also store switch settings and component positions. Over time, ECUs can acquire and store information about the vehicle’s operating characteristics and driver/occupant preferences. The data stored in memory can have a direct affect on how well the vehicle operates and the driver’s perceptions of comfort and convenience.
Types of ECU Memory
Volatile memory chips are the type that require constant power to maintain what is stored in them. When the power is removed, their memory contents are erased. These types of memory chips are used for ordinary microprocessor memory. (RAM for example.) Non-volatile memory chips retain their contents even when the power is removed. These types of memory chips permanently store the microprocessor’s operating instructions, or logic. (ROM for example.) Programmable Read Only Memory (PROM) – A memory chip that can be programmed once, but cannot be reprogrammed. Erasable Programmable Read Only Memory (EPROM) – A programmable chip that can be removed from its circuit and reprogrammed. Electrically Erasable Programmable Read Only Memory (EEPROM) – A programmable chip that can be electrically erased and reprogrammed without removing it from the circuit.
Technical Training
19
Technician Handbook
673 Electronic & Computer Controlled Systems
ECU Customization Because ECUs have memory, they can be programmed with owner/driver preferences.
A
Would you like the interior light turned ON when the doors are unlocked?
B C
Would you like the interior light turned ON when the ignition is turned OFF?
Main Body ECU ECU Memory A. Yes
Customization
B. Yes C. 30 seconds
How long would you like the interior lights to be left ON?
No matter how carefully automobile manufacturers analyze the features that new car buyers want, there will always be those who want a feature to work differently. ECUs have made it much easier for owners to customize many of the vehicle’s convenience features to suit their own preferences. The settings for customizable features are stored in ECU memory. Needless to say, if the memory is lost then any preferences the owner has chosen are also lost. Memory can be lost when the ECU loses its connection to the battery, and also when the ECU is replaced.
SERVICE TIP NOTE
20
Before disconnecting the battery, make note of the owner’s customized settings and restore those settings when service is complete. When one driver changes a customized setting without informing other drivers, another driver may view the change in operation as a malfunction. Be sure to consider the potential role of customized settings on a customer’s concern before beginning a problem diagnosis.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
ECU Initialization Initialization procedures can be very different depending on the ECU. Examples Headlamp Leveling ECU Initialization
Driver’s Door Power Window Initialization (Body ECU)
• Unload the vehicle
• Turn ignition ON
• Jumper terminals 4 and 8 of DLC3
• Hold the switch to open the window
• Flash the headlights 3 times
• Hold the switch to close the window • Keep holding the switch until the switch stops blinking
Completely Closed
Initialization
ECUs may need to be initialized when: • A new ECU is installed • Key components related to the ECU’s operation have been replaced • Loss of power erases critical memory settings. Initializing an ECU simply means preparing it for operation. If an ECU is not initialized when required: • The system may be inoperable or operate incorrectly • Some system features may be disabled.
Why Initialize?
When an ECU is installed, it becomes part of a system of interconnected components. Many ECUs are designed to work in systems with optional components in sometimes varying configurations. Before the ECU can begin operation, it must learn the configuration of the system it’s connected to, and sometimes obtain data from other components. This takes place during initialization. When initialization is completed, the ECU has acquired the information it needs to begin performing its function. In quite a few vehicle systems, ECUs control motors, such as power window motors and power back door motors. These systems require initialization in particular so the ECU can synchronize itself with the motor to control the opening and closing function properly. In systems with jam protection, this feature may be inoperable until the ECU has been initialized.
NOTE
Technical Training
Before determining an ECU is faulty, first verify that it doesn't just need to be initialized.
21
673 Electronic & Computer Controlled Systems
Technician Handbook
This Page Intentionally Left Blank
22
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 2 Topics
Overview of Multiplex Communication
Technical Training
• Why Use Multiplexing? • How ECUs Communicate • Communication Protocols • Multiplex Topology • Single Wire vs. Twisted Pair
23
673 Electronic & Computer Controlled Systems
Technician Handbook
Why Use Multiplexing? One multiplex circuit does the work of many conventional circuits. • • • • • • •
Fewer wires Lighter wiring harnesses Simpler, more reliable wiring Fewer components Fewer connections Lower cost Self diagnostics
Applications of Multiplexing
Multiplexing (or MPX) is a method for communicating between multiple components over a single one-wire or two-wire communication line. Without multiplexing, inter-module communication requires dedicated, pointto-point wiring between all components resulting in bulky, expensive, complex, and difficult-to- install wiring harnesses. Using multiplexing reduces the number of wires by combining many signals on a single wire. Control modules use the data received to control functions such as anti-lock braking, turn signals, power windows, dashboard displays, and audio systems.
Benefits of Multiplexing
In-vehicle networking provides a number of benefits: • Each function requires fewer dedicated wires, reducing the size of the wiring harness. This yields improvements in system cost, weight, reliability, serviceability, and installation cost. • Common sensor data, such as vehicle speed, engine temperature, etc. are available on the network, so data can be shared, thus eliminating the need for redundant sensors or multiple connecting wires. • Networking allows greater vehicle flexibility because functions can be added through software changes in the ECU. Without multiplexing, systems require an additional module or additional terminals for each function added.
24
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
What is Multiplexing (MPX)? Multiplexing is a way to use one wire to communicate between many devices. Conventional wiring between components Light
Motor
Heater
Solenoid Switch Discrete signals L
M
H
Light
S
Motor ECU
MPX communication line
ECU Heater
Solenoid Switch
Multiplexing
In conventional electrical circuits, each voltage signal between components requires its own dedicated wire. The presence, absence, or amount of voltage on the wire (supplied by a switch or a sensor, for example) controls the operation of a component on the other end. In a multiplex circuit, a computer chip on one end of a single wire can transmit a series of coded voltage signals that can be interpreted by a computer chip on the other end. The computer chips are inside electronic control units (ECUs), and the coded voltage signals are data packets. A data packet may instruct the receiving ECU to: • Turn on a light • Start a power window motor • Activate a solenoid Because the data packets are sent in series, multiplexing is also referred to as serial communication or serial networking, and the communication line is called a serial data bus.
Technical Training
25
Technician Handbook
673 Electronic & Computer Controlled Systems
How ECUs Communicate ECUs communicate by sending voltage pulses in a coded sequence. ECU Logic Circuit: • Controls the ON/OFF signal • “Reads” the data on the MPX line • Performs self diagnosis
ECU To communication line: • Supply voltage when transistor is OFF • Ground voltage when transistor is ON Voltage Supply 0v Time
ECU Communication
In the ECU, a switching transistor in the logic circuit controls the transmitting of multiplex signals. When the transistor is OFF, no current flows. Referring to the diagram above, if you were to measure the available voltage on the communication line, you would find supplied voltage. When the transistor is turned ON, current flows and all of the available voltage is dropped across the resistor. Now the voltage measurement on the communication line (after the resistor) is ground voltage. By turning the transistor ON and OFF in a timed sequence, the ECU can send a message to another ECU, similar to sending a message in Morse code. Part of the message, called a data packet, indicates which ECU the message is addressed to. Other ECUs listening to these messages ignore the ones not intended for them.
NOTE
26
The ECU communication line is powered through a resistor that acts as a load in the circuit. This is commonly called a pull-up resistor. If the circuit is grounded, the resistor protects the ECU from damage.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Signaling Between ECUs When one ECU signals another, the one sending the signal is not necessarily the one supplying the power to the circuit. Sender Supplies B+ ECU
ECU
12V
Sends signal
Receiver Supplies B+ ECU
ECU
12V
Sends signal
Signaling Between ECUs
Technical Training
In diagnosing ECU controlled circuits, don’t make the assumption that the ECU sending a signal is the one supplying the circuit voltage. As shown in the illustrations above, it’s possible for the ECU receiving a signal to be the one providing power to the circuit.
27
Technician Handbook
673 Electronic & Computer Controlled Systems
Communication Protocols A “protocol” is the set of rules and standards for communication between components. Protocol
BEAN (TOYOTA Original)
CAN (ISO Standard)
LIN (Consortium)
AVC-LAN (TOYOTA Original)
Application
Body Electrical
Power Train
Body Electrical
Audio
Communication Speed
10 kbps
500 kbps (HS)* 250 kbps (MS)
20 kbps
17.8 kbps
AV Single Wire
Twisted-pair wire
AV Single Wire
Twisted-pair wire
Drive Type
Single Wire Voltage Drive
Differential Voltage Drive
Single Wire Voltage Drive
Differential Voltage Drive
Voltage
10+ volts
2.5v to 3.5v CANH 2.5v to 1.5v CANL
8 volts
2v to 3v TX+ 2v to 3v TX-
Configuration
Ring/Daisy Chain
Bus
Star
Star
Sleep/Wake-up
Available
Available
Available
N.A.
Communication Wire
BEAN: Body Electronics Area Network * Up to 1 Mbps CAN: Controller Area Network LIN: Local Interconnect Network AVC-LAN: Audio Visual Communication - Local Area Network
Communication Protocols
The rules and standards for transmitting and receiving data packets between ECUs are called a protocol. Some protocols provide faster exchange of messages between components and more reliable operation than others. As speed and reliability increases, so does the cost. The chart above compares some of the characteristics of the different protocols found in Toyota vehicles. • BEAN is the earliest protocol used by Toyota. Based on early technology, it is also one of the slowest protocols. BEAN is typically used for body electrical systems such as lights, locks, windows, and air conditioning. • AVC-LAN is another early protocol developed by Toyota as a faster alternative to BEAN for audio, video, and navigation components. • CAN, the ISO standard for automotive applications, is a high-speed protocol for critical vehicle systems such as engine control, braking, precollision, and SRS systems. • LIN is an alternate, low-speed standard protocol developed in later years and used by many manufacturers. Because it is a common standard, it is slightly lower in cost, and because it is a newer standard, it is slightly faster than BEAN. In later model Toyota vehicles, LIN replaces BEAN for control of some body electrical systems such as windows and seats.
NOTE
28
Network speeds are measured in bits per second (bps). A “bit” (represented as ON or OFF, or 0 or 1) is the smallest unit of the code used in a data packet. Kbps stands for kilobits (1000 bits) per second. Mbps stands for megabits (one million bits) per second.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Multiplex Topology Bus Style All ECUs are connected to a single common communication line.
Daisy Chain Style The ECUs are connected in a combination ring and bus form. ECU
ECU ECU
ECU ECU
ECU
ECU
ECU
ECU
ECU ECU
Applies to CAN ECU
Applies to LIN and AVC-LAN
ECU
Master ECU
Applies to BEAN ECU
ECU
Star Style Each ECU is connected directly to a master ECU with a central control function.
Multiplex Topology
Topology describes the pattern of physical connections between components on a network. This may also be called network architecture. Multiplex networks can be configured in a variety of designs. Toyota networks are arranged using primarily three styles: the bus, the ring, and the star. • Bus. In the bus style, multiple ECUs are connected to a single common communication line, allowing each ECU to transmit or receive signals directly with any other ECU on the network. • Ring. ECUs connected in a ring have two network lines to provide a backup path for communication. If one communication line is disconnected, the ECU can still receive network communications on the other line. • Star. The star style uses a central ECU called a master to control the other ECUs in the network (slaves). In this configuration, slaves cannot communicate directly with one another without passing the message through the master. • Daisy Chain. Sometimes a multiplex circuit can combine two design types. An example is a BEAN circuit with both ring and bus topologies.
NOTE
Technical Training
Components on a network are referred to as nodes. ECUs are not the only possible nodes. Sensors with multiplex communication capability can also be nodes on a network. Examples are steering angle sensors and yaw rate sensors.
29
Technician Handbook
673 Electronic & Computer Controlled Systems
Ring Topology In a ring network, a single open circuit in the loop does not affect performance.
Communication lines (bus)
One open wire does not affect network operation.
Ring Topology
30
When network components are connected in a ring, every component has two paths for sending messages to another component. The advantage of ring topology is added reliability because the network continues to operate normally in the event of an open wire anywhere in the multiplex circuit.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Ring Topology Two open connections in a ring network isolates part of the multiplex circuit and sets a DTC.
Communication lines (bus)
Two Opens in a Ring Network
When one ECU sends data to another, the receiving ECU typically sends back a message that it received the data. When a ring network experiences two open wires in the ring, one or more of the ECUs in the network become isolated from the others. An isolated ECU does not receive messages and cannot acknowledge them. The lack of response from an ECU may cause a diagnostic trouble code (DTC) to be set. By studying the network topology and identifying the location of the unresponsive ECUs, you can determine which legs of the circuit contain the open wires.
Technical Training
31
673 Electronic & Computer Controlled Systems
Technician Handbook
Star Topology A single open in a star network isolates only one component.
Master ECU
Open in a Star Network
32
In a star network, the master ECU has a separate communication line to each of the other ECUs. An open in any connection affects only one ECU and does not affect the entire network.
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Bus Topology The effect of an open in a bus network depends on the location. An open on the main bus line isolates part of the network.
An open on a sub bus (branch line) isolates only the component on that branch.
Open in a Bus Network
In a bus network, each ECU is connected to a common communication line called the main bus. An open in the main bus divides the network into two segments. The ECUs that are still connected together in one segment can communicate among themselves but cannot communicate with ECUs in the other segment. The connection between an ECU and the main bus is called a sub bus (or branch line). An open in the sub bus isolates only the ECU on that branch.
Technical Training
33
Technician Handbook
673 Electronic & Computer Controlled Systems
Single Wire vs. Twisted Pair Communication Wire
Feature
Twisted-pair Wire
This communication line is a pair of twisted wires. Communication occurs by applying Hi or positive (+) and Lo or negative (-) voltages to the two lines in order to send a signal (Differential Voltage Drive).
AV Single Wire
This communication wire is thin and lightweight compared with the Twisted-pair Wire. Voltage is applied to this line in order to drive the communication (Single Wire Voltage Drive).
for BEAN, LIN, etc.
Differential Voltage Drive Hi
Single Wire Voltage Drive
Hi
ECU
ECU
Lo
Single Wire vs. Twisted-Pair
ECU
ECU
Lo
Communication over a multiplex line consists of a series of voltage pulses that form a pattern of bits interpreted as data by the receiving ECU. In a typical multiplex system, the voltage pulses are carried over a single wire. In some multiplex systems (CAN and AVC-LAN for example), a pair of twisted wires carry matching pulses—one positive and one negative. This method reduces electromagnetic interference or noise and is more reliable in circuits requiring a greater degree of transmission reliability. For additional reliability and protection from voltage being induced by nearby wiring, some systems use twisted-pair wires with added shielding (AVCLAN, for example).
34
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Advantage of Twisted-Pair Wiring Single Wire Voltage Drive
Differential Voltage Drive 3.5 V
4.0 V
2.5 V
0V
1.5 V
Data
0 1 0
1
Data
0 1 0 1
Noise
Noise
0 1
0
?
Abnormality
Advantage of Twisted-Pair Wiring
Cancel Each Other 0 1
0
1
Electromagnetic interference from nearby wiring can induce unexpected voltage spikes (noise) in a multiplex communication line which alters the coded data being transmitted. The receiving ECU has a way of detecting the data has been altered, but it then has to send a request to the sending ECU to retransmit the data. This slows down communication between the ECUs. To keep high-speed networks operating at high speed, twisted-pair wires provide protection from induced noise. When a network that is wired with twisted pair wiring experiences noise, the abnormality affects each wire in the same way, so the effect of the interference is cancelled out.
Technical Training
35
673 Electronic & Computer Controlled Systems
Technician Handbook
This Page Intentionally Left Blank
36
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 3 Topics
Signals & Waveforms
Technical Training
• Types of Waveforms • Amplitude • Frequency • Pulse Width • Duty Cycle
37
Technician Handbook
673 Electronic & Computer Controlled Systems
Types of Waveforms “Signaling” between circuits and ECUs relies on changes in voltage. When changing voltage is displayed over time, the result is called a “waveform.”
Examples
Digital Voltage
Analog Voltage
Sine Wave
Square Wave Voltage
Time
Voltage
Time
Triangular Wave
Rectangular Wave Voltage
Time
Time
Voltage
Pulse Wave Time
Electronic Communication
Complex Wave Time
Electronic and computerized components communicate with each other using electrical signals. Signals can be as simple as the presence or absence of voltage or current on a wire (ON/OFF signal). Signals can also be as complex as a series of 64 voltage pulses (bits) in a data packet containing precise instructions for a receiving ECU to execute. In all cases, it is changing voltage that contains the information for controlling electronic components. When changing voltage is displayed on a graph of voltage versus time, the resulting pattern is called a waveform.
Types of Waveforms
Electronic circuits produce many different common waveforms. Voltage smoothly changing between a low and a high value produces a sine wave. It is often a change in the signal’s amplitude or frequency that conveys information. A square wave is a digital version of a sine wave. (Digital circuits typically just turn voltage on or off instead of smoothly changing voltage the way analog circuits do.) When the amount of time the voltage is high is different from the time the voltage is low, a rectangular wave results. In this type of signal, it can be the ratio between the two times that controls the component. When voltage changes momentarily and then returns to a steady state again, the result is a single pulse, or a pulse wave. Both square and rectangular waves can be viewed as a repeating sequence of voltage pulses. Any sequence of pulses may be referred to as a pulse train. Audio and video signals appear as randomly changing voltage. Data packets flowing between ECUs also appear as random signals. These types of signals produce complex waves.
38
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Amplitude Amplitude: The difference in voltage between two points on a wave.
Voltage 14 v
Sine Wave
Peak-to-Peak Amplitude = 28 v
0v -14 v Time Voltage 14 v
Square Wave
Peak-to-Peak Amplitude = 14 v
7v 0v Time
Note: Voltage scales can vary.
Waveform Measurements Amplitude
Signaling between electronic components is determined by the characteristics of waveforms and the ways in which they change. Therefore it’s important to understand the different types of waveform measurements. Looking at a graph of a waveform, amplitude is simply the difference in height (voltage) between two points on the graph. Two points often compared are the highest and lowest points. This is peak-to-peak amplitude. Many electronic circuits have a normal operating range. In a circuit with a normal operating range of 0 to 5 volts, for example, waveforms will normally have an amplitude of no more than 5 volts above zero. A signal on such a circuit having a 12-volt positive amplitude could indicate a short to another circuit.
Technical Training
39
Technician Handbook
673 Electronic & Computer Controlled Systems
Frequency Frequency: Number of times a repeating waveform cycles per unit of time.
Voltage
Voltage
1 cycle
Time
1 cycle
Time
Cycle = 10 millisecond (ms)
Cycle = 0.5 second
Frequency = 1 / .010 second
Frequency = 1 / 0.5 second
= 100 times per second (100 hertz or 100 Hz)
= 2 times per second (2 hertz or 2 Hz)
Note: Time scales can vary.
Frequency
When a waveform has a recurring pattern, the pattern repeats a certain number of times per second. The number of times it repeats in a second is its frequency in hertz. •One hertz (Hz) equals one cycle per second. •One megahertz (MHz) equals one million cycles per second. In some applications, it is the frequency of a signal that contains the information. A wheel speed sensor is an example. A passive wheel speed sensor creates a sine wave as the wheel rotates. As the wheel rotates faster, the sine wave’s frequency increases proportionately. An active wheel speed sensor, on the other hand, creates a square wave. As the wheel turns faster, the square wave’s frequency also increases. In both cases, the ECU uses the signal’s frequency to calculate speed.
NOTE
40
Revolutions per minute (RPM) is a type of frequency. 6000 RPM is equivalent to 100 cycles per second (100 Hz).
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Pulse Width Pulse Width: The time duration of a voltage change before it returns to a normal level. Because the pulse widths are different, some ECUs would interpret pulse A as having a different meaning than pulse B. Voltage
Pulse A
Voltage
Time
1 ms. pulse
Pulse B
Time
3 ms. pulse
Pulses can also be negative.
Voltage
Time
Pulse Width
One component can send a signal to another with a voltage pulse. In this case, it is the duration of the pulse, or pulse width, that conveys information. In late-model vehicles for example, tapping the horn switch quickly sends a voltage pulse over the BEAN network to the Body ECU. • A 13 ms. pulse causes the horn to sound for 106 ms. • A 30 ms. pulse also causes the horn to sound for 106.ms. • A 100 ms. pulse causes the horn to sound for 173 ms. • An 8 ms. pulse does not cause the horn to sound at all. In this example, the ECU sounds the horn for a pre-calculated length of time based on the width of the pulse (duration of the voltage signal) from the horn switch.
Technical Training
41
Technician Handbook
673 Electronic & Computer Controlled Systems
Duty Cycle Duty Cycle: The percentage of time that a circuit is ON.
Voltage
10 ms
• Ground-side controlled circuits are ON when the voltage is low. Time
75% 25% 10 ms Voltage
• Power-side controlled circuits are ON when the voltage is high.
25% 75%
Duty Cycle
Time
When voltage alternates repeatedly between a high and a low value, the ratio of time the voltage is high compared to the time it is low can be used to control components. The ratio is called the duty cycle. An example is in controlling the brightness of the dashboard illumination. Older vehicles used a variable resistor to increase or decrease voltage to the lamp to make it brighter or dimmer. In electronic circuits, a modulator can turn a circuit on and off hundreds of times per second. If the amount of time the circuit is ON equals the amount of time the circuit is OFF, the lamp is receiving 50% of the power it would receive if the circuit were just left ON. When the ON time equals 50% of the complete cycle, it is referred to as a 50% duty cycle. Similarly, when the ON time equals 75% of the complete cycle, it’s a 75% duty cycle
42
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 4 Topics
Measuring Signals
Technical Training
• The Oscilloscope • PC Oscilloscopes • Basic Operation • Oscilloscope Scales • Repeating vs. Changing Patterns • Scope Pattern Comparison • Trigger Function • Advanced DVOM Features • WORKSHEET: DVOM Advanced Features
43
Technician Handbook
673 Electronic & Computer Controlled Systems
The Oscilloscope
Voltage
Voltage
The oscilloscope displays voltage in graphical form, indicating how the voltage changes over time.
Time
• The vertical axis represents voltage. • The horizontal axis represents time.
The Oscilloscope
An oscilloscope’s basic function is to display a rapidly changing voltage signal as a graph over time. Oscilloscopes have long been used to analyze engine ignition and fuel systems where signal frequencies are related to engine RPM. With the introduction of automotive ECUs and multiplex circuits, oscilloscopes have now become important tools in diagnosing body electrical systems as well.
44
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
PC Oscilloscopes Originally, oscilloscopes were standalone measuring devices.
In recent years, oscilloscopes have been created for use on PCs or laptop computers.
Required test leads or cables are not shown for either scope.
PC Oscilloscopes
Technical Training
Until recently, oscilloscopes have been standalone measuring devices with some type of display to show the changing voltage pattern. Newer oscilloscopes don’t have their own display, but instead connect to a personal computer (PC) or a laptop computer where they can use the computer screen to display the waveforms.
45
Technician Handbook
673 Electronic & Computer Controlled Systems
Basic Operation When the test leads are connected to the circuit: • The scope repeatedly draws a trace across the screen from left to right.
Voltage
• The trace moves up or down as circuit voltage changes.
A vertical control determines the voltage scale.
Time A timebase control determines how fast the trace is drawn and the time scale.
Basic Operation
An oscilloscope has test leads similar to a DVOM. The leads are connected in a circuit where you want to measure a signal. When operating, the scope draws a line, or trace, across the display screen corresponding to the voltage it is reading. As voltage increases or decreases, the line moves up and down the screen as it is traced. To keep the line from going off the top or bottom of the display screen, a vertical control adjusts the voltage scale so the trace stays on-screen. A similar control adjusts the time scale.
46
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Oscilloscope Scales Signal voltage and frequency can vary widely. • To properly view a signal, the voltage and time scales must be set appropriately.
Square wave
Same square wave, poor time scale 5 V/Div
5 V/Div 12 V
Volts per Division
10 ms 5 ms
10 ms/Div
1 ms/Div Time per Division
Oscilloscope Scales
An oscilloscope screen is divided by horizontal and vertical lines called divisions. When setting the display screen’s voltage scale, you specify how many volts you want each division to represent. In the example above, the signal voltage changes by 12 volts from low to high. The voltage scale in the screen in the illustration has only five divisions. To keep the signal trace from disappearing off the top of the screen, the technician has set this voltage scale to 5 volts per division (5 V/DIV). Other settings are possible (6 V/DIV, for example) that can also keep the entire signal visible. Sometimes it requires a little experimentation to see which scale makes the signal easiest to evaluate. Setting the time scale appropriately is also important for being able to see a signal. In the first example above, the time scale has been set to 10 milliseconds per division (10 ms/DIV). This scale makes the signal’s 20 ms cycle very apparent. In the second example, a time scale of 1 ms/DIV zooms too far in so that only a tiny, unchanging snippet of the signal is visible. Once again, other appropriate time scale settings are possible (20 ms/DIV, for example) that can also display the signal characteristics clearly. If settings aren’t specified for the signal you're monitoring, it may take some experimentation to find the best time scale setting.
Technical Training
47
Technician Handbook
673 Electronic & Computer Controlled Systems
Oscilloscope Scales The Repair Manual provides the appropriate scales for specific signals. Compressor Lock Signal Terminal No. (Symbols) J19-8 (LOCK) – J19-14 (GND)
Tool Setting 200 mV/DIV, 10 ms/DIV
Condition Engine is running Blower switch LO A/C switch ON
CANH Communication Signal Terminal No. (Symbols) J19-11 (CANH) J19-14 (GND)
Tool Setting 1 V/DIV, 10 μsec/DIV
Condition Ignition switch ON
2007 Tundra
Repair Manual Suggested Scales
When following troubleshooting procedures in the Repair Manual, specific settings for the voltage and time scales are often provided to eliminate the need to experiment. It's best to use these provided settings for comparing the signals you observe on your scope display to those illustrated in the “Terminals of ECU” section of the Repair Manual.
48
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Repeating vs. Changing Patterns If the pattern is not repeating, the trace appears noisy at any scale. The voltage does not follow a pattern. As each new trace is drawn on the same screen, the pattern appears “noisy.”
Trace 1
Start
100 ms Trace 2
101 ms
200 ms
100 ms
Trace 3
201 ms
Repeating vs. Changing Patterns
300 ms
20 ms/Div
When a voltage signal is changing rapidly, the oscilloscope trace has to redraw itself on the screen many times per second. In the example illustrated above, the time scale is set to 20 ms/DIV so the entire display represents 100 ms or 1/10 of a second. Therefore, the screen display will be retraced 10 times per second. The signal this scope is measuring, however, is not the type that has a repeating pattern. Looking at the first three 100 ms traces shown on the left, each trace is different. When those traces are drawn on the same oscilloscope screen all within 3/10 of a second, it’s impossible to see any pattern in the overlapping traces. The result is what appears to be a “noisy” signal. This type of signal pattern is common in audio systems.
Technical Training
49
Technician Handbook
673 Electronic & Computer Controlled Systems
Capturing Waveforms You can examine a non-repeating waveform by capturing it. 300 ms of signal captured in scope memory
Start
300 ms 101 ms
200 ms
100 ms view
Scroll to view
Capturing Waveforms
If it’s necessary to see exactly what’s happening in a signal that is not repeating, many oscilloscopes offer a capture feature. When a waveform is captured, a designated time period of signal is recorded in memory so it can be played back and examined in detail. The specifics of how this feature operates vary with different model oscilloscopes. In general, however, the more memory available for recording, the longer the time period that can be captured and the greater quantity of captures that can be kept in memory at one time. Two of the advantages of PC oscilloscopes are a large memory and removable storage media for saving captures.
50
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Scope Pattern Comparison These patterns were captured 3 seconds apart. Trace 1
CAN Network Signal (Low)
Trace 2
Signals are not identical, but they are good signals. How do the traces above compare to what is shown in the Repair Manual? Hint: If in doubt, compare pattern to a known good vehicle.
Scope Pattern Comparison
Multiplex communication signals are prime examples of signals that do not have a repeating pattern. The timing and width of the voltage pulses vary depending on the content of the messages the ECUs are trying to send over the network. Compare the signal to a conversation between people. In natural speech, you wouldn’t expect to see the same sentence repeated at a regular frequency. For that reason, when comparing scope patterns to specifications in the Repair Manual, the comparisons are not likely to be exactly the same. In the case of the CAN low signal, the key observation is that the voltage varies between 1.5V and 2.5V and that the pulses indicating active communication are visible.
Technical Training
51
Technician Handbook
673 Electronic & Computer Controlled Systems
The Effect of Scale These are traces of the same signal. Trace 1
CAN Network Signal (Low)
Repair Manual
Trace 2
0.3 V/DIV
0.5 V/DIV
10 μsec/DIV
50 μsec/DIV
Why do these traces look so different?
When examining or comparing scope patterns, be aware of how small differences in scale can completely alter the signal appearance. NOTES:
52
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Trigger Function A trigger function synchronizes the traces for a stable pattern. • When the trace reaches the right edge of the screen, it has to return to the left side to start another sweep. • To synchronize the traces, the trigger delays the next sweep until the trigger event occurs.
2v 1v 0v -1 v
The trace ends with voltage going negative • If the next sweep starts immediately, it won’t synch with the signal already on the screen. • The display will drift or appear noisy.
This trigger is set to restart the sweep when voltage crosses 1V going positive.
All scopes have a trigger function which is necessary for stabilizing the scope pattern. NOTES:
Technical Training
53
Technician Handbook
673 Electronic & Computer Controlled Systems
Other Trigger Uses The trigger function can also delay capturing a waveform until: A signal appears
Begin capturing when voltage goes over 0.1 volt.
An intermittent fault occurs
Begin capturing when voltage goes over 2v.
A trigger can also be set for capturing a waveform when a specified condition occurs. NOTES:
54
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Advanced DVOM Features Relative Delta
MIN/MAX Recording Mode 1
4
current reading as a Press
2
1
to begin recording
2
Stores the
3
Press
reference value and zeroes the display
4
to pause recording
3
Press and hold to toggle between 100ms and 1ms sampling speeds
Advanced DVOM Features
Some types of electrical measurements that are commonly made using an oscilloscope can be made using the advanced features of many DVOMs. The following are features of the Fluke 87.
MIN/MAX Recording
When voltage is varying, sometimes the only measurements needed are the upper and lower voltage readings. On a CANL communication line, for example, communication signals create voltages between 1.5V and 2.5V. With the MIN/MAX Recording feature, the DVOM records and displays the minimum and maximum voltages to verify the voltage range. MIN/MAX is also helpful for identifying transient voltage spikes. If a momentary 12V spike were to appear on the CANL communication line, the 12V MAX reading would indicate a problem.
NOTE Peak MIN/MAX
Relative Delta
Technical Training
Set the voltage range before selecting MIN/MAX. If auto-ranging sets the initial range too low, the MAX readings will be O.L. By pressing the Peak MIN/MAX button (also called the “alert” button), you can toggle the sampling speed between 100 milliseconds and 1 millisecond. Any voltage signal lasting at least as long as the sampling speed is recorded. The Relative Delta function allows you to select a reference value, and then displays the difference between the current reading and the reference value. This might be useful when looking for variations in voltage from a reference value. In bench testing for resistance, touching the leads together and selecting Relative Delta effectively deducts the resistance of the leads from component resistance measurements.
55
Technician Handbook
673 Electronic & Computer Controlled Systems
Advanced DVOM Features
Positive Trigger
Frequency and Duty Cycle 1
Press
3
- 074.9
1 cycle
%
once
to measure frequency Press
2
again
1
to measure duty cycle
75% duty cycle
Press
Negative Trigger
to toggle between positive and negative trigger for duty cycle
3
2
Changes between + and – to indicate trigger direction
Frequency Measurement
Duty Cycle
1 cycle
25% duty cycle
If you only need to determine a signal’s frequency, you could use the frequency measuring feature available with an advanced DVOM. It measures frequency by counting how many times per second a varying voltage or current reading crosses a selected threshold. Similarly, some DVOMs can calculate duty cycle by measuring the percentage of time a signal is above or below a selected threshold during one cycle. The result is displayed as a percentage. The percent duty cycle reading assumes the first part of the cycle is the ON portion. The value will be different depending on whether the cycle is interpreted as starting with a positive-going (rising) or negative-going (falling) voltage. In a ground-side controlled circuit, the load is ON when the voltage is low. Therefore you want to set the cycle to start when the voltage falls so the percentage of ON time is measured properly. This requires setting the DVOM for a negative trigger. While measuring duty cycle on the Fluke 87, you can toggle between positive trigger and negative trigger by pressing the Peak MIN/MAX button.
56
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheet DVOM Set-up & Advanced Features Classroom Worksheet: In this worksheet you will use a DVOM and a signal generator to measure signals for voltage, frequency and duty cycle.
Use this space to write down any questions you may have for your instructor. NOTES:
Technical Training
57
Technician Handbook
673 Electronic & Computer Controlled Systems
Demonstration Instructor Demo Using DVOM Resistance Setting The instructor will demonstrate using a resistance measurement to measure frequency and duty cycle in the SI circuit of a blower motor. B+
Steering Pad Switches
Blower Motor
IC*
SI
AC Amplifier Varying duty cycle (voltage) regulates motor speed
M
*The integrated circuit (IC) not only drops the voltage for the SI circuit, it also protects the motor from a short in the SI circuit.
Use this space to write down any questions you may have for your instructor. NOTES:
58
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 5 Topics
Using a PicoScope™
Technical Training
• Introduction • Auto Features • Voltage and Time Scale Settings • Turning the Trigger On • Setting the Trigger • Start and Stop Capturing • Horizontal Zoom • Rulers
• Sample Rate • Displaying Two Channels • Separating the A-B Traces • WORKSHEET: PicoScope Basic Setup • WORKSHEET: Using DVOM & PicoScope • DEMO: PicoScope & Power Window Circuit
59
673 Electronic & Computer Controlled Systems
Technician Handbook
Introduction to PicoScope™
• Oscilloscope software on a PC • Hardware connected to PC via USB cable • 1-channel, 2-channel and 4-channel models
Introduction to PicoScope™
Connecting the Leads
PicoScope™ is a brand of PC-based oscilloscope. The PicoScope hardware connects to a personal computer via a USB cable and requires PicoScope software on the PC to display the scope signals. It is available in 1-channel, 2-channel and 4-channel models. Each channel has a lead wire that can be connected to a circuit to be monitored. Various lead connectors are provided for conveniently connecting3 to pins, wires or terminals. The accessory kit also includes inductive clamps for measuring current flow in wiring without disconnecting the circuits. When the leads and hardware are all connected, the PicoScope software running on the PC controls all of the PicoScope’s measurement and display functions.
60
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Auto Features In Auto mode, the scope selects a voltage range that best matches the signal’s peak-to-peak voltage.
The Auto Setup button allows the scope to select both the voltage and time scale.
PicoScope Features
Auto Voltage Scale
As with most software programs, the PicoScope software has a great variety of features. This section introduces the features you will use most frequently. To learn about additional features, refer to the PicoScope manual included in the kit. It can also be referenced within the software program by clicking on Help. Because the frequency and amplitude of different signals vary widely, there is not a single setting of voltage and time scale that will display all signals well. One of the challenges in using a traditional oscilloscope is dialing in the signal, which involves trying different voltage and time scale settings until the signal is displayed clearly. To dial in a signal more quickly, the Auto feature automatically selects the voltage scale that best displays the signal's peak-to-peak voltage. This provides a waveform that is completely captured within the display, and allows the setting to be fine tuned if necessary.
NOTE Auto Setup
Technical Training
The Auto voltage scale feature does not try to set an optimum time scale. You will likely need to adjust the time scale to properly display the signal. The lightning bolt icon selects Auto Setup which not only selects the voltage scale, but also the time scale. These automatic settings usually bring a signal into view, but are often not the best scales for observing it.
61
Technician Handbook
673 Electronic & Computer Controlled Systems
Voltage & Time Scale Settings Drop-down menus display the available settings for the voltage and time scales.
Voltage choices define the range of the entire screen.
Manual Voltage Scale Settings
Time choices define seconds per division. The screen has 10 divisions.
To compare signals to those shown in the Repair Manual, you must manually set the voltage scale. In the Repair Manual, the suggested voltage scale settings are expressed as volts per division. The drop-down menu for selecting the voltage scale on the PicoScope, however, offers choices that define the range of the entire screen. Therefore it’s necessary to make a simple conversion. If the Repair Manual suggests 2 V/Div and the PicoScope screen has 10 divisions, then the desired voltage range is 2 x10 = 20V. A +10V scale would provide a range of 20 volts from -10V to +10v. If the signal actually fluctuates between 0V and 12V, however, part of the waveform will be going off the screen. In such a case, make an adjustment to the voltage scale setting as needed to display the entire signal (+20V).
Manual Time Scale Settings
The PicoScope does not have an auto time setting, so you will have to manually select the appropriate scale. The drop-down menu in this case does give choices in seconds per division, so no conversion is necessary when using Repair Manual recommendations. If you don’t have a recommended time scale and the signal is unfamiliar, look at the waveform at a very high setting and a very low setting. Seeing the signal from both extremes helps you determine the appropriate scale.
62
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Turning the Trigger ON Setting the trigger properly can stabilize a signal pattern, or set the scope to capture a signal only when it goes in or out of a specified range.
Turning the Trigger On
If a pattern is sliding left and right or moving too fast to be seen, setting the trigger can stabilize the waveform. With the trigger on, the signal is not traced on the screen until a specified trigger event occurs. The trigger mode can be set to: Auto – The scope waits for a trigger event before capturing data. If there is no trigger event within a specified time, it captures data anyway. It repeats this process until you click the Stop button. Auto mode does not set the trigger threshold automatically; you must do this manually. Repeat: The scope waits indefinitely for a trigger event before displaying data. Then it waits for another trigger event, and displays the data. It repeats this process until you click the Stop button . If there is no trigger event, it displays nothing. Single: The scope waits once for a trigger event, then stops sampling. To make it repeat this process, click the green START button. The trigger can also be very useful in capturing spikes or other unusual circuit activity. To capture an intermittent fault, set the trigger to start capturing only when the voltage goes out of range.
Technical Training
63
Technician Handbook
673 Electronic & Computer Controlled Systems
Setting the Trigger B
A
D
C
F
E
A. Advanced Triggers – Access a selection of advanced triggers on certain scope devices. B. Trigger Channel - Selects a channel as a source for the trigger. C. Rising Edge – Trigger when a signal crosses the threshold in the rising direction. D. Falling Edge - Trigger when a signal crosses the threshold in the falling direction. E. Threshold – The voltage level that the signal must cross to trigger a capture. F. Pre-Trigger – The amount of data captured before the trigger event (as a percentage of the total capture time).
Setting the Trigger
When the trigger event occurs, the scope begins displaying the signal. The three most important trigger settings are: Threshold – Capture begins when the signal reaches this voltage. Not having this threshold set appropriately is the easiest way to get unsatisfactory trigger results. It must always be set manually. Rising or Falling Edge – This selection specifies whether capture starts when the voltage signal crosses the threshold voltage while rising or while falling. Trigger Channel – When measuring two or more signals simultaneously, you must specify which channel to watch for the trigger event.
64
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Start and Stop Capturing While capturing, the display changes as the signal changes. When stopped, the last capture is frozen.
Start or resume capturing
Stop capturing
Start and Stop Capturing
When you have a lead connected and start the PicoScope software, the screen displays a constantly updated real-time voltage reading. If the voltage is changing rapidly, you will see a rapidly changing waveform. Depending on the signal, you may be able to obtain the information you need from examining the moving waveform. For example, on a CANH bus line, you’re principally looking for a signal that fluctuates rapidly between 2.5V and 3.5V. In some cases, however, you may need to freeze the signal so you can look at the wave pattern more closely. To freeze the signal, click on the red STOP icon in the lower left corner. To resume capturing, click on the green START icon.
NOTE
Technical Training
Pressing the spacebar on the keyboard also stops and starts capturing.
65
Technician Handbook
673 Electronic & Computer Controlled Systems
Horizontal Zoom 1x zoom
Horizontal zoom magnifies the graph in the horizontal direction.
8x zoom
The screen can be scrolled left and right to locate and examine locations of interest.
Horizontal Zoom
Notice the very compact waveform in the upper-right screen above. The time scale setting in that example captured a large number of cycles. The long time setting and large number of cycles were necessary in that case to clearly show the recurring glitches in the signal. To more closely examine these abnormalities in the signal, expand the waveform using the horizontal zoom function. Depending on the point at which the waveform is expanded, however, the abnormality may not be visible. To see it, a scroll bar at the bottom of the screen (not shown above) allows you to scroll left and right to view any part of the captured signal. To return to the original view, reset the scale to x1.
66
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Rulers – Measuring Cycle Duration
510 ms
694 ms
184 ms
Calculates the time between the rulers.
Drag the white box to the right to move the rulers onto the screen. Rulers
Calculates frequency 1/Δ
Rulers
5.43 Hz 5.43 Hz
1/Δ
20 Hz
The software provides rulers to make obtaining accurate time and voltage measurements easier. Vertical Rulers (Time) – To place a vertical ruler at any point on the screen, click and drag the small white box in the lower left corner. Two rulers are available. The ruler measurements and difference between them appear in a box at the top of the screen. A typical use for vertical rulers is to measure the duration of one cycle. The duration of a cycle can be converted into frequency by dividing the duration (must be in seconds) into 1. Example: 1 =
5.4 hertz (cycles per sec.)
.184 sec./cycle Whenever the vertical rulers are used, the PicoScope automatically performs the frequency calculation and displays the result in the lower right corner of the screen.
Technical Training
67
Technician Handbook
673 Electronic & Computer Controlled Systems
Rulers – Measuring Peak-to-Peak Voltage
Drag the blue box down to move the rulers onto the screen.
Calculates the voltage between the rulers.
Rulers
Rulers (Cont’d)
Horizontal Rulers (Voltage) – To place a horizontal ruler at any point on the screen, click and drag the small blue box in the lower left corner. Two rulers are available. The ruler measurements and difference between them appear in a box at the top of the screen. Horizontal rulers are typically used for measuring a signal’s peak-to-peak voltage.
68
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Sample Rate The scope attempts to capture the number of samples per second specified here. Use the up/down arrows to change the setting. Settings range from 50 per second (50 S) to 200,000,000 samples per second (200 MS). The actual number of samples could be different.
Sample Rate
To display a voltage signal that is rapidly changing, the oscilloscope must take sample voltage measurements very frequently. If samples are not taken rapidly enough, the displayed signal will not accurately represent the actual signal pattern. In most cases, a fairly high sample rate displays the signal in detail. In some cases, however, too much detail makes unimportant noise in the signal visible. Reducing the sample rate may filter out the unwanted detail so the fundamental wave pattern is clearer..
Technical Training
69
Technician Handbook
673 Electronic & Computer Controlled Systems
Displaying Two Channels B-Channel ruler B-Channel trace To turn on the B channel, select a voltage range from the pull down menu. B-Channel voltage scale
Displaying Two Channels
Viewing two signals at the same time can be very helpful in a variety of diagnostic situations. With a two-channel or four-channel scope, the additional channels are turned on and off using each channel’s voltage scale setting. To distinguish the different signals, they are color-coded. Voltage scales are displayed on both the left and right sides of the screen. You can set different voltage scales for each signal, but the time scale is the same for all signals.
70
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Separating the A-B Traces To separate the traces:
Click and drag the voltage scale upward
Click and drag the voltage scale downward Or click here for this dialog box
Separating the A-B Traces
In many cases, overlapping signals can make it difficult to analyze the waveforms. Separating the waveforms is as simple as clicking on the voltage scale and dragging it up or down to reposition the signal on the screen. Another way to offset the traces is to click on the colored box in the lower left or right corner. This brings up a dialog box that allows adjustments to scale and offset. To return to the default setting, click on the button with the “return” arrow on it.
Technical Training
71
673 Electronic & Computer Controlled Systems
Technician Handbook
Printing, Saving and Sending Patterns Use the File menu to print or save the current waveform. Once a file is saved, it can be transmitted electronically the same as any other file.
Printing, Saving and Sending Patterns
If your diagnostic efforts require you to print a waveform, use the File menu in the upper left corner to access the printer functions. Use the same File menu if it’s necessary to save a captured pattern. Make note of the folder where the saved file is stored so that you can retrieve it later when needed. Sending a saved waveform file is the same as sending any other file. Note that if the recipient does not have PicoScope software, be sure to save the waveform in a format they will be able to open.
72
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Worksheet (1 of 2) In-class PicoScope: Basic Set-up Classroom Worksheet: In this worksheet, you will set up the PicoScope to measure signals from a signal generator and practice using the PicoScope features to display signal patterns.
Use this space to write down any questions you may have for your instructor. NOTES:
Technical Training
73
673 Electronic & Computer Controlled Systems
Technician Handbook
Worksheet (2 of 2) Using DVOM & PicoScope Shop Worksheet: In this worksheet you will: • Locate and back probe a dimmercontrolled interior lamp or LED • Practice measuring Voltage (V), Hertz (Hz), percentage values (%) using a DVOM • Use the PicoScope to display the signal pattern.
Instructor Demo PicoScope & Power Window Circuit The instructor will demonstrate measuring and displaying signals using the PLS1 and PLS2 signals of a Power Window System.
Use this space to write down any questions you may have for your instructor. NOTES:
74
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 6 Topics
Using an Inductive Clamp
Technical Training
• Inductive Clamp • Preparation for Use • Converting Measurements to Amps • Amp Clamp Applications • WORKSHEET: Inductive Clamp I Measurement & Conversion • WORKSHEET: Inductive Clamp II - Monitor A/C Blower Motor
75
Technician Handbook
673 Electronic & Computer Controlled Systems
Inductive Clamp An inductive clamp measures current flow without opening the circuit. Current flowing in a wire creates a magnetic field around the wire. Magnetic field
Current flow
An inductive clamp placed around the wire measures the strength of the magnetic field to determine current flow.
Wire
Right hand rule determines the direction of the magnetic field.
The Inductive Clamp
An inductive clamp is an accessory that can be used with a DVOM or oscilloscope to measure current. It may also be called an amp clamp or a current clamp. The inductive clamp operates on the principles of magnetism and induction. Electrons flowing in a wire generate a magnetic field around the wire. If another wire or conductor is placed in the magnetic field, the magnetic force causes electrons in the second wire to flow. This is called electromagnetic induction. The strength of current flow and the strength of the magnetic field are directly proportional. The inductive clamp takes advantage of this principle by placing a probe around a wire where it can measure the strength of the magnetic field and thus determine the current flow.
Polarity
The direction of the induced magnetic field depends on the direction of current flow through the wire. If you were to wrap your right hand around the wire with your thumb pointing in the direction of current flow, your fingers would then circle the wire in the direction of the magnetic field. This is called the right hand rule. Because the magnetic field has a polarity, it’s possible to obtain negative readings if the clamp is placed on the wire backward. If this occurs, simply reclamp the wire with the clamp flipped over.
76
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
High Current and Low Current Clamps Use a high current inductive clamp on large wires and circuits with high current flow.
For smaller wires and lower current circuits, use the low current inductive clamp.
Note: Each inductive clamp is rated according to its maximum current measuring capability.
Current Rating
Each inductive clamp is rated according to its current measuring capability. Ratings can vary from 10 amps to 2000 amps. As a safety feature, low current clamps often have jaws that do not accommodate very large gauge wiring. A typical low current clamp is rated between 10 and 60 amps. High current clamps have larger jaws for larger gauge wires. A typical high current clamp is rated between 100 and 600 amps. Very high current clamps may be rated between 1000 and 2000 amps. In general, the higher the current rating is, the less precise the measurements are.
Technical Training
77
Technician Handbook
673 Electronic & Computer Controlled Systems
Preparation for Use After each use, capacitance in the clamp can store a charge that will make the next reading inaccurate.
Clamp (jaws)
To dissipate the stored charge, press to open the jaws and let them snap shut several times. Then zero the tool to cancel the effect of any residual magnetic field.
Preparation for Use
Though there are a wide variety of inductive clamps for DVOMs and oscilloscopes, their basic operation is similar for almost all models. The clamp has a a set of jaws that can be opened and placed around a wire to be measured. After each use, capacitance in the clamp can store a charge that will make the next reading inaccurate. To dissipate the stored charge, open the jaws and let them snap shut several times. Next, press the zero button on the clamp to calibrate the reading and cancel the effect of any residual magnetic field.
NOTE
78
The inductive clamp has an internal battery. Turn the clamp OFF when not in use to keep the battery from discharging completely.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Converting Measurements to Amps When an inductive clamp is used with a DVOM, the meter must be set to measure voltage Convert the voltage reading to amps using a conversion factor.
The sensitivity switch on the clamp specifies what conversion factor to use. 10mV / 1A
45mV
100mV / 1A OFF (e.g. slide switch)
At 100mV / 1A, the 45mV reading equals 45/100 = 0.45A
Note: Not all clamps have a sensitivity switch, but all clamps have a conversion factor.
Converting Measurements to Amps
An inductive clamp actually measures magnetic field strength, not current flow. Therefore when an inductive clamp is used with a DVOM, the meter is set to measure voltage. Most amp clamps have a switch to set the clamp for high or low sensitivity appropriate to the current being measured. The switch is labeled with a millivolts-to-amps ratio needed to convert the DVOM millivolts reading into amps. Different clamps may express conversion factors differently: •10mV / 1A and 100mV / 1A are based on common units of 1 amp. •1mV / 100mA and 1mV / 10mA are based on common units of 1mV. When expressed in common units of 1 amp, the conversion formula is: mV measured A
= 100mV (or 10mV, depending on scale)
When expressed in common units of 1 mV, the conversion formula is: mA
=
mV measured X 100 mA (or 10 mA, depending on scale)
Technical Training
79
Technician Handbook
673 Electronic & Computer Controlled Systems
Amp Clamp Applications Locating short circuits and finding parasitic draws: Clamp a group of wires at a time.
85mV
When current is found, narrow it down to one wire. 85mV
Amp Clamp Applications
One of the disadvantages of the amp clamp is that current measurements are not very precise. Precision varies with the quality of clamp. Readings may be 20% to 50% off from actual when measuring current below 100 milliamps. The great advantage of an amp clamp, however, is that you don’t have to open the circuit to measure current. This is exceptionally helpful in diagnosing short circuits and parasitic draws where the precise current value is not important. The problem with opening circuits while diagnosing shorts and parasitic draw is that power interruptions can launch startup cycles for a variety of ECUs. It can be some time before these ECUs quiet down. Until then, current may be flowing temporarily in many circuits and masking the problem circuit. Another problem with opening circuits is that cycling power may reset a component that was drawing current and may temporarily “fix” the problem.
Diagnosing Short Circuits and Parasitic Draw
When diagnosing a short circuit or parasitic draw, the first objective is identifying the circuit with unexpected current flow. Then your objective is tracing current flow through the wiring until the current flow stops or you find the failed component. • After determining the most likely place to begin, start by clamping a harness or groups of wires to detect which has current flow. • If current is found in the harness or group, test each wire individually to find the active wire. • Use the EWD to follow the wire through junction blocks and connectors to find the problem source.
80
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Amp Clamp Applications Diagnosing intermittent motor failures using an oscilloscope: Starter Motor Current Vehicle being diagnosed:
Known good vehicle:
Diagnosing Motor Faults with an Oscilloscope
The PicoScope and many other oscilloscopes have amp clamps available as optional equipment. One of the applications of an amp clamp and oscilloscope is in diagnosing motor faults. One of the problems with motors on the verge of failure is they exhibit intermittent faults. Resistance in windings or contacts may fluctuate for an extended period before degrading to the point of complete failure. These fluctuations are not revealed in typical DVOM readings. An oscilloscope’s high speed measurements, however, can detect fluctuations in current caused by internal variations in motor resistance. Comparing the current signal pattern to a known good vehicle can reveal if a motor is starting to fail.
NOTE
Technical Training
With many oscilloscopes, using an amp clamp does not require converting millivolts to amps. The oscilloscope can be set to apply the correct conversion factor and display the result in amps.
81
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheets Inductive Current Clamp I: Measurement & Conversion Classroom Worksheet: Some Inductive Current Clamps use a conversion factor for sensitivity. In this worksheet you will practice using the conversion factor to convert voltage to an amperage value.
Inductive Current Clamp II: A/C Blower Motor Shop Worksheet: In this worksheet you will monitor the A/C Blower Motor amperage using a DVOM equipped with an Inductive Current Clamp.
Use this space to write down any questions you may have for your instructor. NOTES:
82
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 7 Topics
Multiplex Circuit • Additional Properties of MPX Protocols Diagnosis
ECU
DLC 3
Technical Training
ECU
Hi
LO
ECU
• BEAN Networks • LIN Networks • CAN Networks • AVC-LAN Networks • Gateway ECUs • Transmit/Receive Charts • BEAN Diagnosis • WORKSHEET: BEAN Network Diagnosis • DEMO: Diagnosing a BEAN Circuit
• LIN Diagnosis • WORKSHEET: AC LIN Interface • CAN Diagnosis • WORKSHEETS: CAN Network Diagnosis (3) • AVC-LAN Diagnosis • WORKSHEET: AVC-LAN Inspection • Other MPX Circuits • WORKSHEET: A/C Bus Servo Motor Operation
83
673 Electronic & Computer Controlled Systems
Technician Handbook
Additional Properties of MPX Protocols Protocol: A set of rules and standards for communication between networked components. Protocols establish the standards for a variety of possible network properties.
Properties: Conventions Communication Direction: One-way, two-way Transmission Timing: Periodic, event-driven Collision Detection & Recovery: Retransmission delay, priority scheme Data Casting: Broadcast, unicast, multicast Sleep Mode & Wake-up Function: Available, not available
Additional Properties of MPX Protocols
The network protocols in Toyota vehicles include: • BEAN • CAN • LIN • AVC-LAN Each protocol defines the rules and standards necessary for components on the network to communicate with one another. Their rules and standards describe various network properties and their conventions. This section discusses some of these properties and typical conventions in more detail.
84
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Communication Direction One-way or two-way One-way communication (mainly used for Door Bus)
Switch Signal (e.g. P/W Open) Data
Power Window Master Switch
Main Body ECU
Transmitter
Receiver
Two-way communication
AC Compressor ON Data Data
Engine ECU Transmitter Receiver
Communication Direction
• Water Temp • Ambient Temp.
A/C ECU Transmitter Receiver
Communication direction is one of the considerations in multiplex network design. Toyota networks may communicate in either a one-way direction or a two way direction. The directional design provides for two different situations: In one-way communication, one component transmits data to another and waits for an acknowledgement. In the example above, the Power Window ECU transmits data to the Main Body ECU that the power window switch is open. The Main Body ECU only acknowledges receipt of the transmitted data. Two-way data transmission involves data flowing in both directions – not just data and acknowledgement, but actual data in both directions. In the example above, the Engine ECU transmits data related to the A/C compressor’s ON status and the A/C ECU acknowledges receipt of that data and replies with additional data related to the water and ambient temperature. BEAN communication direction can be either one-way or two-way. The CAN, LIN, and AVC-LAN are all two-way communication networks.
Technical Training
85
Technician Handbook
673 Electronic & Computer Controlled Systems
Transmission Timing Periodic and event-driven Periodic Transmission Data which always needs to be updated is sent to participating ECUs periodically. Water Temp. Water Temp. Sensor
W
W
Engine ECU
W
W
W
Meter ECU
Event Transmission Data is sent to participating ECUs when any of the relevant switches are operated. ON OFF
S
Power Window Master Switch
Switch Operation
S
Main Body ECU
If a switch is operated during periodic data transmission, a switch operation signal is inserted between periodic data. Periodic data transmission resumes after event transmission. W S
W
S
W
W
S
W
W
Power Window Master Switch
Engine ECU
Main Body ECU
Meter ECU
Page 86
Transmission Timing
Another network property taken into consideration in design is the transmission timing of the data. Data may be periodically transmitted or it may be event-driven. Periodic data, such as a water temperature signal or engine speed, is transmitted at regular intervals. Event-driven data is transmitted when an event occurs, such as when a switch is thrown.
86
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Collision Detection & Recovery Retransmission delay or priority scheme When two ECUs attempt to transmit data at the same time, a data collision occurs. Data
ECU
Data
ECU
ECU
ECU
ECU
Retransmission delay (BEAN) Each ECU stops transmitting for a predetermined time interval. ECUs resume transmitting one after the other, with the highest priority ECU going first. (10 kbps) Priority scheme (CAN) The ECU with the highest priority message is allowed to continue transmitting. Other ECUs stop until the communication line is no longer busy. (250 to 500 kbps)
Collision Detection
In a multi-master network (such as BEAN or CAN), collision detection is a method of resolving data collisions that might occur when more than one ECU transmits at the same time. Multiple access to the serial data bus allows individual ECUs to function independently and transmit at any time they sense an idle network. If a data collision occurs, the ECUs in some networks (such as the BEAN) each wait for a slightly different predetermined time interval and then resume data transmission. The sequence in which they restart is based on their priority. CAN uses a message priority method for resolving conflicts on the network. When a data collision occurs, the ECU with the highest priority message continues transmitting while the other ECUs stop. The other ECUs can resume transmitting when they detect the communication line is not busy. By not interrupting transmission of the priority message, the CAN protocol is able to operate at faster speeds. Both LIN and AVC-LAN networks are controlled by a master node, so no collisions can occur and arbitration or collision management in the slave nodes is not required.
Technical Training
87
Technician Handbook
673 Electronic & Computer Controlled Systems
Data Casting Broadcast, unicast and multicast Broadcast Communication Data is sent from an ECU to participating ECUs.
ECU
ECU
ECU
ECU
ECU
Transmit
Receive
Receive
Receive
Receive
ECU
ECU
Unicast Communication Data is sent from an ECU to a certain ECU.
ECU
ECU
ECU
Receive
Transmit Multicast Communication Data is sent from an ECU to a group of other ECUs.
ECU
ECU Transmit
Data Casting
ECU
ECU
Receive
Receive
ECU
Another attribute of network protocol is data casting. There are three basic types of data casting methods used. • Broadcast communication where every node on the network receives the data. • Unicast communication where data is only addressed to one node on the network and the address is ignored by the other nodes. • Multicast communication where data is transmitted from one node on the network and addressed to a group of other nodes. The Body Electronics Area Network can transmit data using all three types of data casting methods. The Controller Area Network transmits using broadcast and multicast methods. Individual ECUs can ignore sent data but will send a receipt of data transmission. A CAN Bus Check is a broadcast signal which checks to confirm which ECUs are responding. Replies are returned in the order of reception. Local Interconnect Network transmits using the multicast method. Audio Visual Communication-Local Area Network uses all three.
88
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Sleep Mode & Wakeup Function Available or Unavailable Not all systems have sleep mode. When a system with sleep mode judges that the vehicle is not being used, it stops communication of all ECUs to reduce parasitic current. (BEAN, CAN, LIN) Sleep • IG-OFF • All doors are closed • After a predetermined time the system goes to sleep.
the affected ECU sends a “wake-up” message to other ECUs.
zz
Wake-up signal
ECU
zz
Wake-up During sleep, if any of the relevant switches are operated: • Open the door • Unlock the door, etc.
ECU
zz ECU
ECU
ECU
ECU
What would keep the network from going to sleep?
Sleep Mode
In the BEAN and LIN protocols, ECUs periodically transmit data. This activity uses battery voltage and creates a normal parasitic draw. To reduce parasitic draw when the vehicle is not being used, ECUs enter “sleep” mode after a set time when the ignition is off and the doors are closed. After the ignition has been turned OFF, a CAN node may also enter sleep mode to reduce the power consumption. The transmitter portion of the transceiver module is switched OFF, however the receiver part can remain active to check for activity on the bus.
Wakeup Function
When any network-related switch is operated, the associated ECU “wakes up” and sends a wake up signal to all the other ECUs on the network. In a LIN network, both the master and slaves are able to wake-up the network. AVC-LAN does not have a sleep mode and wake-up function.
SERVICE TIP
• A dead battery from a parasitic draw can be caused by a BEAN, LIN, or CAN network that is not going to sleep. • A network can be kept awake if one of the ECUs on the network is receiving constant input from a faulty switch or sensor. • Circuits operating properly can also keep a network awake - an immobilizer key left in the key cylinder (with ignition off) for example.
Technical Training
89
Technician Handbook
673 Electronic & Computer Controlled Systems
Body Electronics Area Network (BEAN) Topology: • •
Daisy chain configuration to improve reliability in the event of open circuit Single-wire voltage drive (speed = 10 kbps) Theft Deterrent ECU
MPX1
Bus
MPX1
Power Seat ECU
MPX1
Bus
MPX2
MPX2 Driver Door ECU MPX1
MPX1
MPX3
Body ECU
MPX2 MPX2
Passenger Door ECU MPX1
Ring MPX4 2004 Avalon
Body Electronics Area Network
The Body Electronics Area Network (BEAN) is a proprietary network developed by Toyota. It is a low-speed protocol typically used for ordinary body electrical systems such as windows, doors, mirrors, seats, etc. The BEAN uses a combination of the ring and bus styles to network its ECUs. This style of connection is also called a daisy chain. The advantage of a ring configuration is that the ECUs in the ring part of the network can continue to communicate even if there is an open in one area because the transmission can travel via two possible pathways. Even in the ring configuration, if the communication line is cut at more than one point, communication becomes impossible. In recent Toyota systems, however, a back-up bus is provided to maintain limited communications. A backup bus usually links the combination switch, front Controller, and Main Body ECU. Several BEAN networks may be connected to each other via a Gateway ECU or to other networks via the Gateway BEAN also provides the capability for customizing certain system settings using Techstream.
90
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Local Interconnect Network (LIN) Master-Slave Protocol: • • • •
Master sends request for data to the slave The slave responds with data requested Slaves cannot transmit unless requested (except for “wake-up” message) Slaves cannot communicate with each other
Master ECU Slave ECU
Slave ECU
LIN Slave ECU
Speed = 20 kbps
Slave ECU
(e.g. Power Window Master Switch, Sliding Roof ECU, etc.)
Local Interconnect Network
LIN was developed by a consortium of European car manufacturers as a lower cost alternative to CAN. Though its maximum transmission speed is only 20 kbps, its cost is two to three times lower per node. It is typically used to control sensors and actuators in non-critical systems such as windows, doors, seats and air conditioning systems.
LIN Characteristics
The LIN protocol uses an AV (automotive vinyl) single wire in a star topology to create a master-slave configuration. Because each of the slaves are connected directly to the master, nodes may be added to the network without requiring hardware or software changes. In the master-slave configuration, slaves can only communicate with the master, and can send data only after receiving a data request from the master. Because each slave is separately connected to the master, a failure in any part of the network does not affect the rest of the network.
LIN Replacing BEAN
Technical Training
BEAN was developed by Toyota as a proprietary network before industrywide automotive networks were available. Because LIN has now appeared as an industry standard and is also a low-speed, low cost network similar to BEAN, it is replacing BEAN in most newer Toyota vehicles.
91
Technician Handbook
673 Electronic & Computer Controlled Systems
Local Interconnect Network (LIN) Topology: • Master ECU is connected to the CAN network • Master serves as a gateway for up to 64 slaves • Single-wire voltage drive ECU
ECU
CAN (e.g. Main Body ECU)
ECU
ECU
Master ECU Slave ECU
Slave ECU
LIN Slave ECU
LIN Gateway Function
92
Slave ECU
LIN has a multiple slave network architecture with a message identification for multi-cast transmission between any network node. It shares some of the features of an AVC-LAN network except that a LIN master ECU contains a gateway function which has the capability to interface with higher-level networks such as CAN. This feature extends the benefits of networking all the way down to the individual sensors and actuators.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Controller Area Network (CAN) Topology • • •
Bus style with terminating resistors at each end Sub-bus lines connect ECUs and sensors to the main bus line Twisted-pair differential voltage drive J/C No. 2
J/C No. 1 Airbag Sensor Assembly
Meter ECU Yaw Rate Sensor
Steering Angle Sensor
Deceleration Sensor
DLC3
Air Conditioner Amplifier
Main Body ECU
CAN-L SIL CAN-H
Engine ECU (ECM)
Skid Control ECU
Terminating Resistors (120 ohm)
CAN HS = 500 kbps (max 1 Mbps) CAN MS = 250 kbps
Controller Area Network
Certification ECU EPS ECU
: CAN Main Bus Line (High) : CAN Sub-Bus Line (High) : CAN Main Bus Line (Low) : CAN Sub-Bus Line (Low) : Serial Communication Line
The Controller Area Network (CAN) was originally developed specifically for automotive applications by Bosch and later adopted as a standard by the International Standards Organization (ISO). It has since been adapted for use in elevators and medical device applications. Similar to BEAN, multiple ECUs are connected to a common CAN bus. However, CAN is not designed for use in a ring topology, and is limited to a maximum of 13 ECUs on a single network. To accommodate more ECUs, multiple CAN networks can be linked by Gateway ECUs. CAN uses twisted-pair wiring to carry matching high and low voltage signals for reliability and speed. It comes in two varieties– HS (high-speed, 500 kbps) and MS (medium-speed, 250 kbps).
Terminating Resistors
Technical Training
The CAN bus uses 120 ohm resistors at each end of the bus to prevent signals from bouncing back and corrupting communications. Since each bus has two resistors between CAN high and CAN low, the resistance between the two CAN bus lines is approximately 60 ohms.
93
Technician Handbook
673 Electronic & Computer Controlled Systems
Audio Visual Communication – Local Area Network (AVC-LAN) Topology: • Master-slave configuration using differential voltage drive • Broadcast, unicast, and multicast communication Multi Display (Master)
Audio Head Unit Gateway ECU BEAN
Television Camera ECU
AVC-LAN
Steering Pad Switch
Stereo Component Tuner
Navigation ECU
Driver Side J/B ECU
Stereo Component Amp.
Audio and Rear A/C Panel Switch
Speed = 17.8 kbps
Audio Visual Communication Local Area Network
AVC-LAN is a unified standard developed by six companies including Toyota Motor Corporation. The intention was to standardize signals such as audio signals, visual signals, switch indication signals and communication signals. The purpose for the standardization was to avoid the incompatibility that resulted when products from more than one manufacturer were combined in a single multimedia system. When the AVC-LAN is linked to other networks, a Gateway ECU (or a gateway function integrated in another ECU) is needed.
94
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Audio Visual Communication – Local Area Network (AVC-LAN) Control: • Each component has an ID. The one with the lowest ID is the master. Multi Display (Master) ID: 110 Audio Head Unit Gateway ECU BEAN
ID: 190
Television Camera ECU
ID: 280
AVC-LAN
Steering Pad Switch
Stereo Component Tuner
Navigation ECU
Driver Side J/B ECU
Stereo Component Amp.
Audio and Rear A/C Panel Switch
ID: 1F0
ID: 440
ID: 178
ID: 1F4
Note: IDs are hexadecimal numbers
AVC-LAN Protocol
An AVC-LAN system consists of audio units and ECUs that are connected in parallel. Each of these units has a switch to connect the unit to the communication bus. When the ignition switch is turned to the ACC position, the vehicle’ s AVCLAN System Master Unit sends a registration request on the system’s LAN circuit. At that time, the mode control portion of the system transmits a physical address back to the Master Unit. The physical address is a threedigit code designation for each of the components of the system (such as the Navigation ECU, Television Camera ECU, Stereo Component Amplifier, etc.) The mode control portion of the system provides communication traffic control and transmits output ON, and output OFF instructions to each of these units when switching from one operation unit within the system to another. All of the components in the system transmit a logical address from each unit. The logical address is a two-digit code (in hexadecimal) that is assigned to each function for that unit (such as command switch, speaker beep, etc). The mode control portion of the system then verifies the connection and operation of each of the components.
NOTE
The numeric IDs are given in hexadecimal numbers. Hexadecimal is the base-16 number system used by computers where A = 10, B=11, C=12, D=13, E=14, and F=15 In vehicles with a multi display (ID = 110 or 118) , the multi display is the master. In vehicles without a multi display, the radio receiver (ID = 190) is the master.
Technical Training
95
Technician Handbook
673 Electronic & Computer Controlled Systems
Gateway ECUs Some ECUs have an integrated gateway function. If different types of networks connect to one ECU, you can assume it has a gateway function. Skid Control ECU
Yaw Rate Sensor Assembly
Seat Belt Control ECU
Skid Control ECU*
Steering Sensor
Clearance Warning ECU
CAN Movement Control Bus (HS)
Navigation ECU*
Network Network Gateway Gateway ECU ECU
Front Heater Control Panel
ECM
LIN
Television Display*
Rear Heater Control Panel
A/C Amplifier Assembly
Center Airbag Sensor Assembly
Combination Meter Assembly
AVC-LAN
Radio Receiver Assembly
Stereo Component Amplifier Assembly
DLC3
Multi-Display*
CAN V Bus (HS)
LIN Main Main Body Body ECU ECU (with (with gateway gateway function) function)
Certification ECU
Driver Seat ECU
Steering Lock ECU
Multiplex Tilt and Telescopic ECU
Outer Mirror Control
Tire Pressure Warning ECU
Bus Buffer ECU
CAN LIN Power Window ECU
Gateway ECU
Immobilizer Code ECU
Sliding Roof ECU
CAN *: Option
LIN AVC-LAN
MS Bus
2009 Land Cruiser
Components on networks using different protocols can’t communicate directly with one another because they don’t “speak the same language.” To translate and relay messages between networks, Gateway ECUs were developed. A Gateway ECU also serves as the interface between vehicle networks and the diagnostic tester (via the DLC3 connector). In many systems, a major ECU (such as the Main Body ECU) may include a gateway function within it. If different types of networks connect to one ECU, you can assume it also serves as a Gateway ECU.
CAN Gateway ECU
A vehicle may have multiple Controller Area Networks for a variety of reasons. • A CAN bus can have no more than 13 nodes. To link more than 13 components using CAN requires two or more networks. • CAN buses may be different speeds (HS or MS). • Multiple buses are often intentionally used so that a failure in one bus doesn’t disable components on other CAN buses. To link multiple CAN buses together, a CAN Gateway ECU can be used.
96
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Gateway ECU Functions Communication: Provides communication link between multiple buses of the same protocol. ECU
BEAN
Gateway ECU
BEAN
ECU
Diagnosis: Stores DTCs for BEAN networks.
ECU
BEAN
Gateway ECU
BEAN
ECU
DLC3
Interface: Translates messages from one protocol to another.
ECU
BEAN
BEAN
ECU
Gateway ECU ECU
CAN
Summary of Gateway ECU Functions
AVC-LAN
Customize: Enables the customize feature of BEAN networks.
Gateway ECU
DLC3
BEAN Audio
ECU
The Gateway ECU connects buses of different protocols and DLC3, and manages communications between them. It also provides signal conversion between the BEAN, CAN, and AVC-LAN networks. Gateways also regulate the exchange of data between networks of the same protocol, such as two BEAN networks. Separate BEAN networks ensure that a failure in one network won’t disable all BEAN components. BEAN networks are connected to the DLC3 via the gateway and the gateway communicates with the diagnostic tester. The gateway does not interpret the messages; it simply transfers the Diagnostic Requests onto the BEAN and then transfers Diagnostic Responses from the BEAN onto ISO 9141 (the diagnostic protocol). If a malfunction occurs in the BEAN communication, DTCs are stored in the gateway memory. The gateway acts as a kind of firewall to prevent the entire system from being affected if one bus fails. The gateway enables the customize feature of BEAN networks.
Technical Training
97
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Gateway ECU Functions A CAN Gateway ECU has fewer but more specialized functions. Data destined for components on the other bus is relayed.
DTCs are stored in the CAN Gateway ECU.
CAN Gateway ECU
Data not intended for components on the other bus is not forwarded.
CAN Gateway ECU Functions
ECU
ECU
ECU
ECU
ECU
ECU
ECU
Compared to other Gateway ECUs, the CAN Gateway ECU’s functions are simplified: •Forward data from one bus to the other when the data is addressed to components on the other bus. •Restrict transmission of data to the other bus when the data is not addressed to any components on that bus. •Store DTCs for failure in components or communication lines.
98
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Transmit/Receive Charts Air Conditioning System Diagram AVC-LAN
Multiplex Network Body ECU
A/C Amplifier
Combination Meter Assy
Front Controller
BEAN
CAN
Accessory Meter Assy
Transmitter
Gateway ECU
DLC3
ECM ECM
Receiver
Line
Signal Heater Relay Control Signal Magnetic Clutch Control Signal
ECM
BEAN/CAN
Rear DEF Relay Control Signal Idle Up Signal
A/C Amplifier
Pressure Sensor Signal External Variable Control Solenoid Current Signal
Transmit/Receive Charts
Multiplex Network Body ECU
BEAN
Accessory Meter Assy
BEAN / AVCLAN
Diagnostic Tool Response Diagnostic Data Indicator ON demand signal
The transmit/receive charts in the Repair Manual can be very helpful in understanding the operation of a multiplex circuit. The example above is just a portion of the chart for the air conditioning system of a 2005 Avalon. These charts can be found in the System Diagram section of the Repair Manual for each system using multiplex communication.
Technical Training
99
673 Electronic & Computer Controlled Systems
Technician Handbook
BEAN Communication Signal
BEAN Signal
100
BEAN uses a single wire voltage drive protocol. The BEAN communication signal varies from zero to a nominal 10 volts. The circuit is at rest when at zero volts
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis Check DTC information Examples Communication line disconnection or open at 2 points
DTC No.
Detection Item
B1200
MPX Body ECU communication stop
B1271
Combination meter ECU communication stop
Detecting Condition Communication with Gateway ECU stopped 10 sec. or more
Communication line short B1214
Short to B+ in door system communication bus malfunction
When a +B short circuit is detected in the door system communication bus
B1215
Short to GND in door system communication bus malfunction
When a body ground short circuit is detected in the door system communication bus
2008 Avalon
BEAN Diagnosis
The Gateway ECU monitors communication on the BEAN and stores a DTC when it detects a network communication error (DTC B12XX). The Gateway ECU outputs only B12XX DTCs. Note that DTCs indicating “communication stop” typically mean there is a disconnection or open circuit that is isolating one more ECUs from the network. You can determine the possible locations of the open circuit by examining the wiring diagram and analyzing which ECUs are offline. Because short circuits disable the entire network, those DTCs do not identify a particular ECU. The diagnostic procedure for shorts involves disconnecting portions of the circuit until communication resumes. You then know the short is in the disconnected portion of the circuit.
Technical Training
101
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Open Circuit Communication line disconnection or open at 2 points DTC No. B1271
Detection Item
Detecting Condition Communication with Gateway ECU stopped 10 sec. or more
Combination meter ECU communication stop
Defective combination meter ECU power supply or ground
Possible Causes Body Body ECU ECU
Wire harness open circuit
Meter ECU
Failure in Combination Meter ECU
A/C A/C ECU ECU
Open Circuit
Defective inner communication line in each ECU
Gateway Gateway ECU ECU
Connector disconnected
: Communication Circuit
Components connected to the BEAN in a ring style (daisy chain) have two paths for data flow around the ring, so a single open in the network does not stop communication. Two opens in the communication line, however, will isolate one or more ECUs. In the example above, the Combination Meter ECU has become isolated. The potential problem areas are: • A loss of power or ground to the Meter ECU • Failure inside the Meter ECU • Meter ECU connector disconnected • Two opens in the wire harness leading to the Meter ECU • Failures in the internal communication lines of the two ECUs connected to the Meter ECU
102
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit Communication line short DTC No. B1215
Detection Item Short to GND in door system communication bus malfunction
Detecting Condition When a body ground short circuit is detected in the door system communication bus
Body Body ECU ECU
Meter Meter ECU ECU
A/C A/C ECU ECU
Gateway Gateway ECU ECU
The entire network is down due to the short.
: Communication Circuit
Short Circuit
When a communication line is short-circuited to B+, the entire line is 12V, and if short-circuited to ground, it’s 0V. Being unable to vary the voltage on the line, the Gateway ECU cannot communicate with any ECUs so it is impossible for it to determine the location of the short. To locate the short, disconnect each ECU one by one and check what DTC is output.
Technical Training
103
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit (Step 1) Begin by disconnecting the first ECU, then checking if network communication resumes. If network communication resumes after removing the Meter ECU, the short is in this ECU. Meter ECU Body Body ECU ECU
“B” “C”
“A” “D”
A/C A/C ECU ECU If communication does not resume, the short is still in some other part of the network.
Short Circuit Step 1
Gateway Gateway ECU ECU : Communication Circuit
Working around the ring starting with the first ECU past the Gateway, begin disconnecting ECUs one by one. When the ECU with the short is disconnected, network communication will resume. To determine when the network is communicating again, you can connect a DVOM or oscilloscope to the BEAN circuit at the Gateway ECU. When voltage or a signal reappears on the circuit, the most recent component disconnected is the one with the short.. Another way to check for communication is to examine DTCs after an ECU is disconnected. In this example, the Meter ECU is disconnected first. If DTC 1215 (communication line short) is still present, then the Meter ECU is not the problem; the short is still in the part of the circuit connected to the Gateway ECU. Continue to the next step. • If DTC 1271 (Meter ECU stop) occurs, then the short circuit is no longer present in the network and it is working again. This means the short must be in the disconnected Meter ECU. Replace it.
NOTE
104
Don’t disconnect the Gateway ECU because that’s where the DTCs are stored. When DLC3 is connected to the Gateway ECU, disconnecting the Gateway from the rest of the network sets DTCs for all the other ECUs because the Gateway can no longer communicate with any of them.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit (Step 2) If the fault is not found, disconnect the next ECU and recheck for communication. If communication resumes after the Body ECU is disconnected, the short is in harness B” or in the Body ECU. Reconnecting the Meter ECU will tell you where the short is (Step 3). Body ECU
Meter ECU
“B” “C”
“A” “D”
A/C A/C ECU ECU If communication does not resume, the short is still in some other part of the network. Reconnect the Meter ECU, then disconnect the A/C ECU (Step 4).
Short Circuit Step 2
Gateway Gateway ECU ECU : Communication Circuit
Continuing trouble shooting this example, disconnect the next ECU after the Meter ECU and check if the communication signal reappears. If checking DTCs: • If DTC 1215 (communication line short) is still present, then the harness “B” and the Body ECU are not the problem. The short is in the part of the network still connected to the Gateway ECU. Continue to step 4. • If DTC 1271 (Meter ECU stop) and DTC 1200 (Body ECU stop) occur, then the short circuit is no longer present in the network. Since you already ruled out a problem with the Meter ECU, this means the fault must be in the disconnected harness “B” or in the Body ECU. To diagnose which, continue to step 3.
Technical Training
105
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit (Step 3) If fault is found, isolate the location by reconnecting the first ECU and rechecking for communication.
Body ECU
If communication stops when the Meter ECU is reconnected, that means the short is in the harness that was just reconnected to the network. Meter Meter ECU ECU
If communication continues, the short is in the Body ECU that is disconnected from the network.
“B” “C”
“A” “D”
A/C A/C ECU ECU
Gateway Gateway ECU ECU : Communication Circuit
Short Circuit Step 3
To determine if the problem is in harness “B” or the Body ECU, reconnect the Meter ECU. If communication stops, the short is in harness “B”. If communication continues, the short is in the Body ECU. If checking DTCs: • If DTC 1215 (communication line short) occurs again instead of DTC 1200 (Body ECU stop), then the short has been reconnected to the part of the circuit connected to the Gateway ECU. It has to be in harness “B”. Replace it.. • If DTC 1200 (Body ECU stop) remains, the short circuit has been isolated from the network. The only part not connected to the network is the Body ECU. Replace it.
106
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit (Step 4) If the fault wasn’t found, continue isolating the problem by disconnecting the next ECU and rechecking for communication.
Body ECU Meter Meter ECU ECU If communication resumes, the short is in harness “C” or the A/C ECU. Reconnect the Body ECU and recheck for communication (Step 5)
“B” “C”
“A” “D”
Gateway Gateway ECU ECU A/C ECU If communication does not resume, the short is still in part of the network connected to the Gateway ECU
Short Circuit Step 4
: Communication Circuit
Not having found the fault yet, disconnect the next ECU after the Body ECU and recheck for network communication. If communication resumes, the fault is in either harness “C” or the A/C ECU because these two components have been removed from the network. Go to step 5 to determine which component is at fault. If communication does not resume, reconnect the Body ECU, and go to step 6. If checking DTCs: • If DTC 1215 (communication line short) is still present, then the harness “C” and the A/C ECU are not the problem because they are no longer connected to the Gateway ECU. Continue to step 6. • If DTC 1200 (Body ECU stop) and B1262 (A/C ECU stop) occur, then the short circuit is no longer present in the network. This means it must be in the disconnected harness “C” or in the A/C ECU. To diagnose which, continue to step 5.
Technical Training
107
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit (Step 5) If fault is found, isolate the location by reconnecting the previous ECU & rechecking DTCs.
Body Body ECU ECU If DTC 1215, then the short is in the part of the network that was just reconnected to the Gateway ECU.
Meter Meter ECU ECU
“B” “C”
“A” “D”
Gateway Gateway ECU ECU A/C ECU If DTC 1262 (A/C ECU stop), then the short is in A/C ECU.
Short Circuit Step 5
: Communication Circuit
To determine if the problem is in harness “C” or the A/C ECU, reconnect the Body ECU and check for communication. If communication does not resume, the short is in harness “C” that was just reconnected to the network. If communication does resume, the short is in the S/C ECU that is still disconnected from the network. If checking DTCs: • If DTC 1215 (communication line short) occurs again, then you’ve reconnected the short to the communication circuit. Since you already ruled out the Body ECU as the problem, it must be in harness “C”. Replace it. • If only DTC 1262 (A/C ECU stop) is present, then the short circuit is no longer present in the network. This means it must be in the disconnected A/C ECU. Replace it.
108
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis – Short Circuit (Step 6) If the fault wasn’t found, it is in harness “A” or “D,” or in the Gateway ECU.
Body Body ECU ECU
Meter Meter ECU ECU
“B” “C”
“A” “D”
A/C A/C ECU ECU
Gateway Gateway ECU ECU
All other parts of the circuit have been eliminated except “A”, “D” and the Gateway ECU. Test the two harnesses for a short. If no short is found, replace the Gateway ECU.
: Communication Circuit
Short Circuit Step 6
The only remaining locations for the short are in harness “A” or “D,” or in the Gateway ECU. • Test wire harnesses “A” and “D” for a short, and replace if needed. • If the short is not in either wire harness, replace the Gateway ECU.
Technical Training
109
Technician Handbook
673 Electronic & Computer Controlled Systems
BEAN Diagnosis by Split-Half Method When many ECUs are connected to the bus, disconnect half the bus to save time.
ECU ECU “A” “A”
ECU ECU “B” “B”
ECU ECU “C” “C”
ECU ECU “D” “D”
Disconnect
Gateway Gateway ECU ECU
Diagnosing a Large Network
ECU ECU “E” “E”
Disconnect
ECU ECU “I” “I”
ECU ECU “H” “H”
ECU ECU “G” “G”
ECU ECU “F” “F”
Disconnecting ECUs one at a time can be time consuming if the network has a large number of ECUs. To save time, isolate half the network by disconnecting an ECU nearest the Gateway, and another farthest away. • If communication resumes, the short is in the disconnected part of the network. • If communication does not resume, the disconnected ECUs are normal and the short is in the other half. Knowing which half of the network to diagnose, proceed by disconnecting and connecting ECUs one at a time until you find the trouble location.
110
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
BEAN Diagnosis If there is no multiplex communication system DTC, check the relevant ECUs using Techstream. Data List – Check switch or sensor to find: • Switch or sensor malfunction • Malfunction in an ECU input circuit
Active Test – Check actuator to find: • Actuator malfunction • Malfunction in an ECU output circuit
Diagnosis with Techstream
When diagnosing a problem for which there are no BEAN communication DTCs (B12xx), use Techstream to test the ECUs related to the problem for proper function. • Data List enables you to test the inputs to the ECU. If the ECU is not seeing the correct switch or sensor values, you can isolate the problem to the switch/sensor, switch/sensor circuit or the ECU itself. • Similarly, Active Test enables you to test the ECU outputs. This can narrow a problem down to an actuator circuit, an actuator or the ECU.
NOTE
Technical Training
Because BEAN is a slow-speed network, the Data List may update very slowly. To speed results, make a custom list of just those data items being monitored.
111
673 Electronic & Computer Controlled Systems
Technician Handbook
Diagnosing a BEAN Open Circuit
When the signals at two points in the same BEAN circuit are not identical, there is an open between those two points.
Diagnosing a BEAN Open Circuit with an Oscilloscope
When a BEAN network is operating normally, oscilloscope probes can be placed at any point on the network and the signal patterns will be perfectly identical. That’s because the network is continuous and the signal at any point is the same. However, an open circuit in a bus segment of a BEAN network separates the network into two parts. Similarly, two opens in the ring portion of the network also separate the network into two parts. Now the network is no longer continuous. Though separated into two different networks, the ECUs on each half continue to communicate with each other. Being separate networks, however, the communication on each half is now unique. The oscilloscope trace on one half is different from the trace on the other half. Knowing this can help you two ways in diagnosis. • If you find the signals on two points of a BEAN network are different, you know those points are divided by an open circuit (or two). • As you move one of the probes closer to the other, when the signals become identical, you have just passed over the location of the open circuit.
112
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheet BEAN Network Diagnosis Classroom Worksheet: This worksheet introduces you to BEAN network operation and fault diagnosis.
Instructor Demo The instructor will demonstrate how to use the PicoScope for diagnosing a BEAN network.
Use this space to write down any questions you may have for your instructor. NOTES:
Technical Training
113
673 Electronic & Computer Controlled Systems
Technician Handbook
LIN Communication Signal
LIN Signal
114
Similar to BEAN, LIN also uses the single wire voltage drive protocol with a signal voltage range between zero and a nominal 12 volts. The circuit is at rest at the higher voltage.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
LIN Diagnosis Diagnosis is similar to BEAN: • For shorts, disconnect connectors and recheck DTCs. • For opens, follow the DTCs. Immobilizer Immobilizer Code Code ECU ECU LIN (Certification Bus) Main Main Body Body ECU ECU (Instrument (Instrument Panel Panel Junction Junction Block) Block)
Smart Smart Key Key ECU ECU Assembly Assembly
Steering Steering Lock Lock ECU ECU
LIN (Door Bus)
Power Power Window Window ECU ECU
Sliding Sliding Roof Roof Control Control ECU ECU
2008 Highlander HV
LIN Diagnosis
Diagnosing a LIN circuit is similar to diagnosing a BEAN circuit, except LIN does not use a ring or daisy chain configuration. When a communication line is shorted to ground, the network cannot communicate with any ECU. To isolate the location of the fault: • Disconnect connectors and recheck DTCs to isolate the part of the circuit with the short. With an open, DTCs guide you to the circuits to check. Possible causes are: • Connector disconnected • Defective ECU power supply or ground • Open in wire harness • ECU failure
Technical Training
115
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheet A/C LIN Interface In this worksheet you will monitor and diagnose the A/C Control Assembly operation, and LIN communication using the Techstream unit, TIS and a PicoScope.
Use this space to write down any questions you may have for your instructor. NOTES:
116
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Communication Signal CANH: 2.5v to 3.5v
CANL: 2.5v to 1.5v
CAN Signal
Technical Training
CAN uses the two-wire differential drive protocol. The signal on the CAN High (CANH) wire ranges from 2.5v to 3.5V, while the signal on the CAN Low (CANL) wire ranges from 2.5v to 1.5V. Note that the two signals are mirror images with CANH going high (to 3.5V) at the same moment CANL goes low (to 1.5). When both signals are 2.5V, the circuit is at rest.
117
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Diagnosis – Shorts Short between CAN-H and CAN-L:
Short CANH to ground:
No ECUs can communicate.
No ECUs can communicate.
ECU
Main Bus
ECU
ECU
ECU
ECU
ECU
Sub Bus
Short
Short to B+ (CANH or CANL):
Short CANL to ground:
Communication is not reliable.
Communication is not reliable.
ECU
ECU
B+
ECU
ECU
ECU
ECU
Note hyperlinks to circuit traces.
CAN Diagnosis
The CAN bus uses twisted-pair wiring for reliability. At each end of the CAN bus, the wires are connected together by a 120 ohm terminating resistor. The purpose of the resistors is to reduce noise in the circuit. The resistors may be located inside ECUs or junction connectors.
Short Between CANH and CANL
When the bus wires are shorted together at any point on the bus, it is impossible to generate a differential voltage on each wire for communication. Thus, the entire bus goes down.
NOTE
Short to B+ or Ground
Even when the network is down, each ECU continues to attempt communication. If you isolate an ECU from the short and the problem is not in the ECU, an oscilloscope will show it still generating CAN signals. When a connection to B+ brings CANH high, or when a connection to ground brings CANL low, there is still the appearance of communication on the circuit. In the first case, CANL can still be brought low to create a voltage differential, and in the second case, CANH can still be brought high. Though communication on the circuit is compromised, ECUs may still appear in the CAN bus check in either case. On the other hand, bringing CANH low by grounding it, or bringing CANL high with a short to B+ renders the circuit incapable of generating a voltage differential. These are the cases when the ECUs do not show up in the CAN bus check. Wave forms for various short circuit conditions appear in the appendix.
118
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Diagnosis – Opens Open on both CAN-H and CAN-L: On Main Bus: Communication is not reliable on each half of the network. ECU
ECU
On Main Bus: Communication is not reliable.
ECU
ECU
On Sub Bus: Affected ECU can’t communicate. ECU
ECU
ECU
Open in CANH or CANL
Open
ECU
Open on just CAN-H or CAN-L:
On Sub Bus: Communication with the affected ECU is not reliable.
ECU
ECU
ECU
ECU
Open
Note hyperlinks to circuit traces.
Open in CANH or CANL
Opens
When an open occurs on the CAN bus, the effect depends on whether the open is on the main bus line or a sub bus line. An open on the main bus affects the entire bus, but an open on a sub bus line only isolates the ECU(s) on that sub bus.
NOTE
Despite an open, the ECUs connected together are still trying to communicate, but the break in the network introduces considerable noise into the signal. Therefore, communication becomes unreliable. Wave forms for various open circuit conditions appear in the appendix.
Technical Training
119
673 Electronic & Computer Controlled Systems
Technician Handbook
CAN BUS Check
CAN Bus Check
Location of DLC3
Using Techstream to perform a CAN bus check quickly identifies any ECUs that are not communicating. Comparing these ECUs to the multiplex circuit diagram from the EWD can potentially help identify possible problem locations before performing vehicle diagnostics. When analyzing the multiplex circuit diagram to locate the ECUs that are not communicating, also note the location of DLC3. A problem between the network and DLC3 can make it appear the entire network is down. Also, when the vehicle has more than one CAN network, DLC3 is directly connected to only one of them. By analyzing the ECUs that are communicating, you can determine which CAN network is experiencing trouble.
120
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Terminating Resistors Know where the terminating resistors are located.
HS Bus
MS Bus
Disconnecting them will cause network communication to become unreliable.
Terminating Resistors
The CAN high and CAN low communication lines are connected at each end by a terminating resistor. This resistor helps to stabilize voltages on the lines and prevent “echoes.” The terminating resistors are almost always inside two of the ECUs on the network. (In some vehicle models, a terminating resistor may be located inside a junction connector.) As the illustration above shows, disconnecting either of the ECUs containing an HS bus terminating resistor would create an open in the CAN bus and take the bus down. All of the other components on the CAN HS bus are connected by sub bus lines. Therefore these ECUs can be disconnected from CAN without creating an open in the main bus line.
Technical Training
121
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Resistance Tests Check Bus Line (CANH – CANL) A
OK! (54 to 69 Ohm)
B
NG (70 Ohm or more)
C
NG (Less than 54 Ohm)
Check Bus Line (CG – CANH/L) CG – CANH CG – CANL NG
B
Open in CAN Bus Line
C
Short in CAN Branch Line
OK! (200 Ohm or more)
Short of CAN Bus line to CG
OK! Check Communication Malfunction DTC (Past DTC)
A Check Bus Line (CANH/L - BAT) CANH – BAT CANL – BAT NG
OK! (6k Ohm or more)
Short of CAN Bus line to BAT
OK!
Resistance Tests on CAN Circuits
NOTE
Does 60 ohms between CANH and CANL mean the network is OK?
CAN diagnostic procedures in the Repair Manual call for various resistance tests that can be useful in identifying shorts and opens in the bus line. To perform resistance testing on the CAN bus, the ignition must first be cycled OFF. After turning the ignition off, it may take up to several minutes for capacitors to fully discharge and the resistance reading to stabilize. Any readings obtained before the circuit has stabilized will not be accurate. Resistance measurements will change slightly when Techstream is connected to the network via DLC3.
122
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
CAN Resistance Tests ECU
ECU
ECU
• CANH to CANL DLC 3
Hi
LO
• CANH to BAT
CG
CANH
• CANL to BAT • CG to CANH
1 2 3 4 5 6 7
8
• CG to CANL 9 10 11 12 13 14 15 16
CANL
Resistance Tests on CAN Circuits
NOTE
BAT
When it comes time in the diagnostic process to measure the resistance between CANH and CANL, it doesn't take but a few extra moments to obtain all the other resistance measurements, too. Doing so can provide a more complete picture of the bus status before arriving at a conclusion regarding the source of a problem. Before making resistance measurements between the CAN bus and B+ or ground, disconnect the negative battery cable. This prevents obtaining resistance readings through alternate paths. When analyzing resistance measurements, more than one reading may be out of spec. For example, there may be a 73 ohm reading between CANH and CANL and a 0.3 ohm measurement between CANL and CG. If the only measurement taken was the out-of-spec resistance of CANH to CANL, the diagnostic flow chart on the previous page would indicate an open circuit. In reality, an open circuit would create a very high ohm reading. By making the other measurements, the 0.3 ohm reading between CANL and CG suggests a short to ground. This would most likely be the problem rather than the slightly out-of-spec 73 ohm reading between the bus lines.
NOTE
Technical Training
When testing resistance at the DLC3 connector, keep in mind that in models with a more than one CAN bus, the DLC3 terminals may be testing only one of the buses. To test other CAN buses, it may be necessary to use a different connector.
123
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheets (1 of 3) CAN Diagnosis Classroom Worksheet: In this worksheet you will build a strategy to diagnose a CAN network fault using the EWD, a Techstream CAN bus check, and the information provided.
Instructor Demo CAN Resistance Test Precautions In the shop, the instructor will demonstrate how improper methods can result in incorrect CAN resistance measurements.
>>
2006 RAV4 Multiplex Circuit Diagram (PDF)
Use this space to write down any questions you may have for your instructor. NOTES:
124
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Worksheet (2 & 3 of 3) CAN Main Bus Faults Shop Worksheet: In this worksheet you will: • Use an ohmmeter and a PicoScope to observe CAN High and CAN Low • Diagnose a short to ground and an open circuit on CAN High and CAN Low • Short CAN High to CAN Low to observe the results.
CAN Sub Bus Diagnosis Shop Worksheet: In this worksheet you will use the EWD and Techstream’s CAN Communication Bus Check to develop a strategy to diagnose CAN sub bus faults.
Use this space to write down any questions you may have for your instructor. NOTES:
Technical Training
125
Technician Handbook
673 Electronic & Computer Controlled Systems
AVC-LAN Communication Signal Differential Voltage Drive • TX+ (similar to CANH) • TX- (similar to CANL)
TX+ and TX- are both pulled high. The rulers show the differential voltage is greater than 120mV.
2v to 3v
(+5V Scale, 5ms per division, x4 zoom)
AVC-LAN Signal
AVC-LAN uses differential voltage drive similar to CAN. However, the high and low voltage signaling circuits – similar to CANH and CANL - are referred to as TX+ and TX- in AVC-LAN devices. Also similar to CAN, the ends of the TX+ and TX- lines are joined by 120 ohm resistors. Whereas the CAN bus line idles at 2.5V, the AVC-LAN idles at around 2V. When communicating, AVC-LAN pulls the voltage high on both TX+ and TX-. The line voltages have to differ by more than 120mV for the AVC-LAN system to recognize communication.
126
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
AVC-LAN Diagnosis Starting Diagnostic Mode (with Multi Display) Vehicle Condition
Procedure Method 1 While pressing the “INFO” button, alternately turn the light control switch from OFF to TAIL 3 times
• SPD 0 km/h • ACC or IG ON*
*To quit the diagnostic mode, turn to IG OFF.
+
TAIL
OFF
Method 2 While in the display adjustment screen, alternately touch the upper and lower parts of the left side of the screen 3 times
Note: On some vehicles 2010 and beyond, AVC-LAN DTCs can be retrieved using Techstream.
AVC-LAN Diagnosis
Technical Training
Some vehicle models have AVC-LAN that functions independently of any of the other vehicle networks. The AVC-LAN in other models, however, may communicate with other vehicle networks through a Gateway ECU or other ECU with a gateway function. Before diagnosing the AVC-LAN, first be sure any other networks the AVC-LAN connects to are functioning properly.
127
Technician Handbook
673 Electronic & Computer Controlled Systems
AVC-LAN DTCs Code: 01-E0 Logical Address
DTC
Sub-Code: 110-00- 4 Physical Occurrence Address Connection Count Confirmation # Logical Address Navigation ECU 01 = Communication control 58 = Navigation ECU 80 = GPS Receiver Multi Display 01 = Communication control 34 = Front passenger monitor Stereo Component Amplifier 01 = Communication control 61 = Cassette tape player sw. 63 = On-dash CD changer
DTC E0 = “Registration complete” signal from master device cannot be received
Physical Address 178 Navigation ECU 110 Multi Display 190 Radio and Player 440 Stereo Component Amplifier
Connection Confirmation # • The number of minutes after power-up when the DTC occurred
Occurrence Count • The number of times the DTC has been detected
Note: AVC-LAN codes are vehicle specific. Always check the Repair Manual for the vehicle being serviced.
AVC-LAN DTCs
AVC-LAN has a fairly robust self-diagnostic capability with diagnostic trouble codes consisting of five parts: Logical Address. The logical address code ( a hexadecimal number) does not refer to a component; it refers to a function within a component. The Navigation ECU, for example, has a Navigation ECU function (logical address = 58) and a GPS Receiver function (logical address = 80). Other components have their own unique functions with their own unique logical addresses. An exception is the Communication Control function which every AVC-LAN component has. This function’s logical address is 01. DTC. The DTC is a hexadecimal number that defines the specific problem. For each DTC, the Repair Manual has an explanation of the meaning and the corrective action or additional diagnostic steps. Physical Address. This hexadecimal number corresponds to specific AVCLAN components such as the Navigation ECU, audio head unit, stereo amplifier, multi-display, etc. Connection Confirmation Number. Upon power-up, the AVC-LAN master ECU checks all the slaves once per minute. The connection confirmation number increases by one after every check. When a DTC is detected, the connection confirmation number is included with the DTC information to indicate when the fault occurred in relation to power-up. This can be useful in determining the sequence in which DTCs occurred. Occurrence Count. Provides a count of the number of times a DTC has been detected.
128
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheet AVC-LAN Inspection Shop Worksheet: In this worksheet you will create, monitor and diagnose a Stereo Component Amplifier malfunction involving an AVC-LAN circuit.
Use this space to write down any questions you may have for your instructor. NOTES:
Technical Training
129
Technician Handbook
673 Electronic & Computer Controlled Systems
Other Multiplex Circuits BUS connectors in air conditioning servo motor circuits illustrate the advantages of a simple multiplex circuit. BUS Connector Communication/Driver IC
With Bus Connectors A/C Amplifier Communication IC
CPU
One 3-wire harness A/C M
M
M
M
Pulse-type Servo motors
Without Bus Connectors A/C Amplifier
Servo motors
Drive IC CPU Drive IC
A/C M
Other Multiplex Circuits
M
M
M
Four 5-wire harnesses
Although BEAN, LIN, CAN, and AVC-LAN are the most frequently used multiplex protocols in automobiles, other automotive systems may gain the advantages of multiplex communication by implementing their own special purpose protocols. Dynamic laser cruise control is one example of a circuit that uses serial communication that is not BEAN, LIN, CAN or AVC-LAN. The laser sensor and Distance Control ECU use their own special purpose multiplex protocol because of the complex communication required between them. The significance of knowing this is that when you encounter a circuit described as “serial”, you’ll know to expect a fluctuating communication signal on that line instead of a fixed voltage.
A/C Servo Motor Circuits
An air conditioning servo motor circuit is another good example of using multiplex circuits to reduce wiring. The typical connection between the A/C amplifier and an ordinary servo motor requires five wires: • Two wires to the motor – necessary so forward or reverse current can be supplied to control motor direction. • Three wires to the sensor circuit to determine motor position and direction. To reduce the wiring between the servo motors and the A/C amplifier, pulsetype servo motors use a communications chip built into the servo motor connector. This chip, called a BUS connector, communicates with the A/C amplifier using serial data (multiplex) communications. In this configuration, only three wires are needed: • Power • Ground • Communication signal
130
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
BUS Connectors BUS Connectors with built-in communication/driver ICs allow the use of pulse-type servo motors and require less harness wiring. BUS Connector Communication/Driver IC
With Bus Connectors A/C Amplifier Communication IC
IC
CPU
One 3-wire harness A/C M
M
M
M
Pulse-type Servo motors
Bus Connector
Note: If the color-coded connectors are not matched to the correct servo motors, the wrong motors will operate.
BUS Connectors
The BUS connectors are sequentially arranged on a single harness to yield a bus network topology. Each BUS connector controls its motor’s operation by translating serial data from the A/C amplifier on the communication signal line. It then interprets pulses from the A, B, and GND contacts on the servo motor, converts them into serial data and transmits position information back to the A/C amplifier. All the BUS connectors share the same communication line, so the serial data flowing to and from the connectors must include a connector ID. This ID enables the connector to ignore A/C amplifier signals meant for another servo motor, and enables the A/C amplifier to determine which connector is transmitting its motor position information. Because of this, if the connectors are not matched to the correct servo motors, the wrong motors will operate.
NOTE
131
Some newer vehicles have as many as 12 AC servo motors operating on three unique BUS connector networks. In these vehicles, this special purpose multiplex protocol saves a considerable amount of wiring, contributing greatly to lighter weight, less expense, and greater reliability.
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Pulse-Type Servo Motors Pulse-type servo motors transmit two ON/OFF signals to communicate damper position and movement direction. Contact Points
Printed Circuit Board
A
Servo Motor A B GND
B GND
Conduction A B
High Low
High Low
Pulse-Type Servo Motors
Also called pulse pattern type servo motors, these motors use a printed circuit board that rotates with the motor shaft to signal motor direction and position. As the motor turns, the contact points at A and B open and close a circuit to create a coded pulse pattern that indicates the position of the damper doors. Because the output signals from the motor are digital (ON/OFF), the communication chip that relays these signals does not need to perform analog-to-digital conversion. This makes the communication chip much simpler, smaller, and less expensive.
132
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Worksheet A/C Bus Servo Motor Operation & Diagnosis Shop Worksheet: In this worksheet you will monitor Bus Connector and Servo Motor operation using Techstream DATA LIST and a PicoScope to deduce communication problems with the A/C System.
Use this space to write down any questions you may have for your instructor. NOTES:
Technical Training
133
673 Electronic & Computer Controlled Systems
Technician Handbook
This Page Intentionally Left Blank
134
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Section 8 Topics
Electronic Systems
Technical Training
• Engine Immobilizer • WORKSHEET: Immobilizer System • Power Distributor • Smart Junction Box (MICON) • HID Headlights • Dynamic Laser Cruise Control
135
Technician Handbook
673 Electronic & Computer Controlled Systems
Immobilizer Function Prohibits the engine from starting unless an authorized ignition key is used. ID code stored in key must match code stored in ECU.
Transponder Chip
Key Cylinder
DLC3
Communication
Ignition Transponder Key ECU
Ignition Key Transponder Key Coil Transponder Key Amplifier
Blinks until authorized key is in key cylinder.
Engine Immobilizer Function
ECM
Security Indicator Light
Fuel Disabled until ECM receives “OK” from Transponder Key ECU
The engine immobilizer system is designed to prevent the vehicle from being stolen. When the immobilizer system is set, the ECM disables the fuel delivery and ignition systems. Only an authorized key can unset the immobilizer. The Transponder Key ECU assembly stores the codes of authorized ignition keys. When an authorized key is used to start the engine, the ECU sends a signal to the ECM to unset the immobilizer and permit fuel delivery and ignition.
136
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Immobilizer System Operation Security Indicator Light
ECU Logic 1. Detects unlock warning switch is on when key is in ignition
4
3
2. Activates antenna coil Transponder Key Amplifier
3. Faint electric wave sent 4. Key ID code returned 5. ID code signal amplified and sent to ECU 6. ECU compares key ID code to registered codes.
Antenna Coil
8 2 5
Unlock Warning Switch (Key Cylinder)
1
6 Transponder Key ECU
7
Front Door Courtesy Light Switch (LH)
ECM
If codes match: 7. Cancels immobilizer 8. Turns off indicator light
Engine Immobilizer Operation
When a key is inserted in the key cylinder, the Transponder Key ECU detects the unlock warning switch is closed and sends a signal to activate the antenna coil in the transponder key amplifier. The antenna generates a faint electric wave activating the transponder chip in the key grip to transmit its ID code. The transponder key amplifier receives and amplifies the ID code signal, then transmits it to the Transponder Key ECU. The ECU compares the key’s ID code to the registered codes stored in its memory. If the codes match, the ECU sends a signal to the ECM to unset the immobilizer and switches off the security indicator light.
Key Code Registration
For the immobilizer system to operate, authorized keys must be registered with the Transponder Key ECU. The system provides three types of key code registration procedures. New Key Registration. This procedure is used if the registered master keys are lost, and when the Transponder Key ECU must be replaced for other reasons. An initial set of keys can be automatically registered immediately after the new ECU is installed. Additional Key Registration. New keys (up to a certain total number of keys based on vehicle model) can be added to those already registered in the Transponder Key ECU. Key Code Erasure. For lost keys, key codes can be erased. This procedure erases all codes except the master key. The remaining authorized keys must be reregistered.
Technical Training
137
Technician Handbook
673 Electronic & Computer Controlled Systems
Security Indicator Light No key or unregistered key (keeps blinking)
…
Immobilizer is set
…
Key recognized Master key indication (light goes off)
…
Immobilizer is set
Immobilizer is unset
…
Sub key indication (on for 2 sec.)
…
Master Keys and Sub Keys
Immobilizer is set
Immobilizer is unset
…
The difference between a master key and a sub key is that a sub key cannot be duplicated. This is a security feature that helps customers feel safer about leaving a key with parking attendants. You can distinguish between a master key and sub key by observing the security indicator light when the key is inserted in the ignition switch. • When a master key is placed in the ignition switch. The indicator light turns off. • When a sub key is placed in the ignition switch, the indicator light remains illuminated for 2 seconds before turning off
138
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
Automatic Key Code Registration Indicator codes during automatic key code registration: Blinking: Everything is operating normally
Code 2-2: Key has already been registered
Code 2-1: Registration failed (bad key)
Code 2-3: Maximum number of keys already registered
Automatic Key Code Registration
When the Transponder Key ECU is replaced, the new unit is preset to automatically register keys. To take advantage of automatic key code registration: • After replacing the transponder key ECU, insert the first key into the ignition key cylinder. It takes about one second for the transponder key ECU to register the key’s code. • Remove the key and insert the next key. • Repeat until all keys have been registered.
Watch for Error Codes
If an error occurs during automatic key code registration, the security light blinks a two-digit code: Code 2-1: Key code registration failed, most likely because a code could not be read from the key’s transponder chip. The key should be discarded. Code 2-2: The key has already been registered. Code 2-3: The maximum number of keys have already been registered.
Ending Automatic Registration
Automatic key code registration ends automatically after the maximum number of keys have been registered. If registering fewer than the maximum number of keys, the automatic registration process has to be terminated manually. • Use Techstream to end automatic key code registration. • Turn the ignition switch ON and OFF five times within 10 seconds to force automatic key code registration to end.
NOTE
Technical Training
Failing to terminate key code registration can result in abnormal system operation.
139
673 Electronic & Computer Controlled Systems
Technician Handbook
Configuration in Earlier Models In earlier models, the immobilizer functions are built into the ECM.
2001 Avalon
Configuration in Earlier Models
140
Engine immobilizer was introduced in the 1998 model year. The first vehicles with this feature have the immobilizer functions built into the Engine Control Module. This configuration exists in model years as late as 2004.
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Configuration in Later Models
In later models, the immobilizer functions are controlled by a separate Transponder Key ECU.
2007 Tundra
Configuration in Later Models
Technical Training
In later models, a separate Transponder Key ECU was added to control the immobilizer functions in place of the ECM. The advantage of a separate, special ECU is that it is less expensive to replace than an ECM in the event of lost keys or an ECU malfunction.
141
673 Electronic & Computer Controlled Systems
Technician Handbook
TIS Immobilizer Reset
Immobilizer reset is not supported on all vehicles. Refer to the Support Chart for more information.
Immobilizer Reset
Because of the original system design for the immobilizer function, losing all the keys to the vehicle meant that the ECM or Transponder Key ECU had to be replaced. Later systems were modified so that the ECM or Transponder Key ECU could be reset to accept registration of new keys. Resetting the immobilizer to accept new keys requires obtaining a passcode through TIS. For security reasons, only Master Technicians and MDTs are authorized to request an immobilizer reset passcode. For theft prevention and security monitoring, each time a passcode is requested, it is logged into a national database. Once a passcode is obtained, it’s entered into the ECU through Techstream or a scan tool. When the ECU is successfully reset, the master key in the ignition becomes registered to the vehicle and all previous key codes are erased.
142
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Immobilizer Reset Support Chart From TIS Immobilizer Reset Page
Immobilizer Reset Support Chart
The blue boxes on the support chart indicate which vehicle models have the immobilizer reset feature. The legend at the top of the chart describes applicable TSBs. Immobilizer systems that do not have immobilizer reset are indicated by the white boxes. In these vehicle models, either the Transponder Key ECU or ECM must be replaced if all the keys to the vehicle are lost. In these cases, whether the ECM or Transponder Key ECU must be replaced depends on the system configuration. If the vehicle has a separate Transponder Key ECU, then that is the component that must be replaced. If the immobilizer functions are controlled within the ECM, then the ECM must be replaced. PANT Bulletin GI03-09 (referenced next to the white square in the legend) describes conditions under which the ECU or ECM replacement cost can be subsidized.
Technical Training
143
Technician Handbook
673 Electronic & Computer Controlled Systems
ECM Communication ID Registration In vehicles with a separate Transponder Key ECU, the ECM Communication ID must be registered whenever the ECM or Transponder Key ECU is replaced. CG
TC DCL3 SST Example Procedure: 1. Using SST, connect TC to CG. 2. Turn the ignition switch ON (do not start the engine) and leave it for 30 minutes.
3. Turn the ignition switch OFF and disconnect TC and CG. 4. Check that the engine starts. 2005 Avalon
ECU Communication ID Registration
For security reasons, immobilizer systems with a separate Transponder Key ECU are designed so that the vehicle will not start if either the ECM or ECU have been replaced. This security is provided by a unique ECU communication ID stored in both the ECM and Transponder Key ECU. Therefore, when either unit is replaced, the ECU communication ID has to be registered between them.
NOTE
The code registration procedure described above is an example that may not apply to all vehicles. Be sure to refer to the Repair Manual for the correct procedure for the vehicle being serviced.
144
Technical Training
Technician Handbook
673 Electronic & Computer Controlled Systems
DTC Check/Clear Immobilizer diagnostic methods and procedures may vary between vehicle models. Examples: Vehicle Model
To check DTCs w/check wire on DLC3
To clear DTCs w/o Techstream
2005 Avalon
• TC to CG
• Remove the EFI No. 1 fuse
Yes
2006 Sequoia
• TC to CG for DTC 99 • CG to OP3 for other DTCs
• Remove the ECU-B fuse and EFI No. 2 fuse from the engine room J/B for 1 minute or more.
No
2006 Tacoma
• Not supported
• Not supported
Yes
2006 Tundra
• CG to OP3
• Remove the ECU-B fuse from the driver side J/B for 1 minute or more.
Yes
CG
Techstream supported?
OP3
1 2 3 4 5 6 7 8
DLC3
9 10 111213 1415 16
TC
Be Wary of Differences between Models
While the concepts of immobilizer components and operation are similar among all systems, the specifics of each system can vary significantly. The example above demonstrates how different the diagnostic methods and procedures can be between different models. The bottom line is that when diagnosing the immobilizer system, it’s especially risky to assume that one vehicle model is the same as another. Always refer to the repair manual for the specifics of the vehicle being serviced.
Technical Training
145
673 Electronic & Computer Controlled Systems
Technician Handbook
Transponder Key ECU Input Signals: • • • •
KSW CODE EFII CTY
Output Signals: • • • •
VC5 TXCT IND EFIO
2007 Tundra
Analyzing ECU Input and Outputs
In diagnosing an engine immobilizer malfunction, you may need to verify the Transponder Key ECU is receiving the correct input signals and is sending the correct output signals. Remember that in earlier model vehicles without a Transponder Key ECU, you’ll be verifying the immobilizer system signals flowing into and out of the ECM. You can identify the inputs and outputs using the system description and looking at the wiring diagram and TERMINALS OF ECU section of the Repair Manual. For our example, we’ll be using the 2007 Tundra to illustrate diagnostic concepts. Note that these may not translate exactly to other vehicle models. Inputs: KSW – ignition key cylinder unlock warning switch CODE – key ID code from transponder key amplifier EFII – ECM communication input signal CTY – front door courtesy switch LH (required for registration only) Outputs: VC5 – five-volt power supply to transponder key amplifier TXCT – communication signal to transponder key amplifier IND – security indicator light signal EFIO – ECM communication output signal
146
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Transponder Signals
KSW
VC5
TXCT
CODE
2007 Tundra
Transponder Signals
KSW. When a key is inserted in the key cylinder, the key switch closes. The voltage on KSW drops to zero, alerting the Transponder Key ECU. VC5. The Transponder Key ECU immediately supplies power to the transponder key amplifier so it can operate. TXCT. The Transponder Key ECU commands the transponder key amplifier to begin pulsing for the key code. CODE. The amplifier sends the code to the Transponder Key ECU. After the transponder key amplifier transmits the key code, the Transponder Key ECU stops requesting the code and shuts off the power to the amplifier.
NOTE
Technical Training
The example is for a 2007 Tundra. This does not work exactly the same for all models.
147
673 Electronic & Computer Controlled Systems
Technician Handbook
Transponder Key ECU – Power & Ground
Power & Ground +B to GND: (J26 disconnected) • Always – 11V to 14V
IG to GND: (J26 disconnected) • Ignition OFF – below 1V • Ignition ON – 11V to 14V
GND to Body ground: (J26 disconnected) • Always – below 1Ω
Power and Ground Circuits
148
2007 Tundra
Several of the Transponder Key ECU’s terminals are for power and ground circuits. Diagnosis also involves testing at these terminals to be sure the ECU is receiving the proper voltage and has a good ground.
Technical Training
673 Electronic & Computer Controlled Systems
Technician Handbook
Transponder Key ECU – Input & Output Input KSW to GND: (J26 disconnected) • No key in cylinder – 10KΩ or higher • Key In cylinder – below 1Ω CTY to GND: (J26 connected) • Door closed – 10KΩ or higher • Door open – below 1Ω
Output IND to GND: (J26 connected) • Immobilizer set (blinking) – alternates between 11V to 14V and below 1V • Immobilizer unset (off) – below 1V
VC5 to GND: (J26 connected) • •
No key in cylinder – below 1V Key In cylinder • 4.6V to 5.4V until Transponder Key ECU receives key code (
View more...
Comments
